Asymptomatic uterine incarceration at term gestation: a case report

Uterine incarceration is a rare event complicating pregnancy. Herein, we present a unique case of an asymptomatic term pregnancy with uterine incarceration; this patient had had an anterior myomectomy 3 years earlier. She had an asymptomatic antenatal course and incidental identification of uterine incarceration during cesarean section. We also address the importance of early recognition and appropriate management regarding this circumstance.

2-Keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN)- and N-acetylneuraminic acid-cleaving sialidase (KDN-sialidase) and KDN-cleaving hydrolase (KDNase) from the hepatopancreas of oyster, Crassostrea virginica

KDN (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid), a sialic acid analog, has been found to be widely distributed in nature. Despite the structural similarity between KDN and Neu5Ac, alpha-ketosides of KDN are refractory to conventional sialidases. We found that the hepatopancreas of the oyster, Crassostrea virginica, contains two KDN-cleaving sialidases but is devoid of conventional sialidase. The major sialidase, KDN-sialidase, effectively cleaves alpha-ketosidically linked KDN and also slowly cleaves the alpha-ketosides of Neu5Ac. The minor sialidase, KDNase, is specific for alpha-ketosides of KDN. We were able to separate these two KDN-cleaving enzymes using hydrophobic interaction and cation-exchange chromatographies. The rate of hydrolysis of 4-methylumbelliferyl-alpha-KDN (MU-KDN) by KDN-sialidase is 30 times faster than that of MU-Neu5Ac in the presence of 0.2 M NaCl, whereas in the absence of NaCl this ratio is only 8. KDNase hydrolyzes MU-KDN over 500 times faster than MU-Neu5Ac and is not affected by NaCl. KDN-sialidase purified to electrophoretically homogeneous form was found to have a molecular mass of 25 kDa and an isoelectric point of 8.4. One of the three tryptic peptides derived from KDN-sialidase contains the consensus motif, SXDXGXTW, that has been found in all conventional sialidases. Kinetic analysis of the inhibition of the hydrolysis of MU-KDN and MU-Neu5Ac by 2, 3-dehydro-2-deoxy-KDN (KDN2-en) and 2,3-dehydro-2-deoxy-(Neu5Ac2-en) suggests that KDN-sialidase contains two separate active sites for the hydrolysis of KDN and Neu5Ac. Both KDN-sialidase and KDNase effectively hydrolyze KDN-G(M3), KDNalpha2-->3Gal beta1-->4Glc, KDNalpha2-->6Galbeta1-->4Glc, KDNalpha2-->6-N-acetylgalactosaminitol, KDNalpha2-->6(KDNalpha2-->3)N-acetylgalactosaminitol, and KDNalpha2-->6(GlcNAcbeta1-->3)N-acetylgalactosaminitol. However, only KDN-sialidase also slowly hydrolyzes G(M3), Neu5Acalpha2-->3Galbeta1-->4Glc, and Neu5Acalpha2-->6Galbeta1-->4Glc. These two KDN-cleaving sialidases should be useful for studying the structure and function of KDN-containing glycoconjugates.

Catabolism of asialo-GM2 in man and mouse. Specificity of human/mouse chimeric GM2 activator proteins

Tay-Sachs disease is an inborn lysosomal disease characterized by excessive cerebral accumulation of GM2. The catabolism of GM2 to GM3 in man requires beta-hexosaminidase A (HexA) and a protein cofactor, the GM2 activator. Thus, Tay-Sachs disease can be caused by the deficiency of either HexA or the GM2 activator. The same cofactor found in mouse shares 74.1% amino acid identity (67% nucleotide identity) with the human counterpart. Between the two activators, the mouse GM2 activator can effectively stimulate the hydrolysis of both GM2 and asialo-GM2 (GA2) by HexA and, to a lesser extent, also stimulate HexB to hydrolyze GA2, whereas the human activator is ineffective in stimulating the hydrolysis of GA2 (Yuziuk, J. A., Bertoni, C., Beccari, T., Orlacchio, A., Wu, Y.-Y., Li, S.-C., and Li, Y.-T. (1998) J. Biol. Chem. 273, 66-72). To understand the role of these two activators in stimulating the hydrolyses of GM2 and GA2, we have constructed human/mouse chimeric GM2 activators and studied their specificities. We have identified a narrow region (Asn(106)-Tyr(114)) in the mouse cDNA sequence that might be responsible for stimulating the hydrolysis of GA2. Replacement of the corresponding site in the human sequence with the specific mouse sequence converted the ineffective human activator into an effective chimeric protein for stimulating the hydrolysis of GA2. This chimeric activator protein, like the mouse protein, is also able to stimulate the hydrolysis of GA2 by HexB. The mouse model of human type B Tay-Sachs disease recently engineered by the targeted disruption of the Hexa gene showed less severe clinical manifestation than found in human patients. This has been considered to be the result of the catabolism of GM2 via converting it to GA2 and further hydrolysis of GA2 to lactosylceramide by HexB with the assistance of mouse GM2 activator protein. The chimeric activator protein that bears the characteristics of the mouse GM2 activator may therefore be able to induce an alternative catabolic pathway for GM2 in human type B Tay-Sachs patients.

Structural characterization of gangliosides isolated from mullet milt using electrospray ionization-tandem mass spectrometry

Electrospray ionization (ESI) coupled with tandem mass spectrometry has been used in conjunction with microwave-mediated saponification, periodate oxidation, and clostridial sialidase hydrolysis to enable detailed structural characterization of gangliosides and their derivatives present in mullet milt. The gangliosides extracted from mullet milt were determined to be GM3, GM3 lactone, GM3 methyl ester, and 9-O-acetyl GM3. For the major ganglioside GM3 and all GM3 derivatives, the ceramide composition was revealed to be C18:1/C16:0. GM3 with a C18:0/C16:0 ceramide was also found as a minor ganglioside. Both the ganglioside intramolecular ester and the ganglioside methyl ester (lacking carboxylic acid groups) showed dominant chloride attachment peaks (M + Cl)- in negative ion ESI-MS in addition to low intensity peaks corresponding to (M-H)-. GM3 and O-acetyl GM3 bearing carboxylic acid functions showed only (M-H)-. In positive ion ESI, GM3 and O-acetyl GM3 revealed (M + 2Na-H)+ peaks in addition to (M + Na)+, indicating free exchange of the carboxylic acid proton with a sodium cation, while the ganglioside intramolecular ester and ganglioside methyl ester with no acidic protons yielded only (M + Na)+. The strategy of employing ESI-MS to detect products of established wet chemical reactions represents a general approach for elucidation of ganglioside structural details.

Susceptibility testing and clinical effect of fusidic acid in oxacillin-resistant Staphylococcus aureus infections

One hundred and six oxacillin-resistant Staphylococcus aureus (ORSA) isolates collected from various clinical specimens at Mackay Memorial Hospital during the period from 1997 to 1998 were tested. The MICs of fusidic acid against ORSA isolates were in the range of 0.06 microgram/mL to 4 micrograms/mL. There was only one ORSA isolate (0.9%) resistant to fusidic acid in this study. Twenty-four patients with ORSA infection were enrolled into the study between July 1997 to June 1998. Four patients without the evidence of sepsis received oral fusidic acid only. The other 20 patients with sepsis received intravenous glycopeptide first, and then the oral fusidic acid for 7 to 10 days. Oral fusidic acid was used for mild ORSA infection and achieved satisfactory clinical outcome. In severe ORSA infection, it was found that sequential therapy with fusidic acid had relapsed in three patients. We concluded that oral fusidic acid achieved a satisfactory outcome in our patients with mild ORSA infection. In such cases, fusidic acid may provide an effective alternative treatment of choice. The rare side effect of granulocytopenia and jaundice was noted in our case series. The side effect may be not so rare as previously thought, if it had been carefully looked for.

Psychosocial risk factors of teenage pregnancy in eastern Taiwan

BACKGROUND

Teenage pregnancy is a growing worldwide problem, associated with adolescents' social and health problems and poor perinatal outcome. This study was conducted to investigate psychosocial factors predisposing to the high teenage pregnancy rate in Hualien, eastern Taiwan.

METHODS

A regional hospital-based study was conducted with a retrospective analysis of hospital records and questionnaires to collect personal and family data regarding the perinatal outcome of 100 pregnant teenagers and 100 pregnant adults, who had normal deliveries at the Buddhist Tzu-Chi General Hospital between 1994 and 1995.

RESULTS

A significantly higher percentage of teenage mothers were of aboriginal origin than adult mothers (63% vs 25%; p < 0.05) and lived in rural areas (80% vs 19%; p < 0.05). There was also a higher incidence of late antenatal care (31% vs 11%; p < 0.05) drinking (36% vs 9%; p < 0.05) and a greater history of smoking (34% vs 7%; p < 0.05) among teenage mothers. About 86% of teenage mothers did not use any contraception. The preterm birth rate was not significantly higher in the adult group, but teenage mothers tended to have significantly lower birth weight infants (19% vs 9%; p < 0.05) and a decreased incidence of cesarean section (19% vs 33%; p < 0.05). About 20% of the teenage mothers had their first coitus before the age of 13, while none of the adult mothers had sexual coitus before the age of 13.

CONCLUSIONS

In this hospital-based study, teenage mothers tended to be of aboriginal origin, lived in rural areas, had early sexual exposure without contraception, had drinking and smoking habits, were late seeking antenatal care and gave birth to low birth weight infants.

Laparoscopic loop ligatures for bladder repair during laparoscopic surgery

In this paper, we report a case where a bladder perforation occurred during a laparoscopically assisted vaginal hysterectomy and was repaired by laparoscopic loop ligatures. This is the first case report of using the laparoscopic loop ligatures to close the bladder perforations. The loop ligature is an easy and quick procedure, which can be performed by most surgeons who take the time to learn the endoscopic suturing techniques.

The structural basis for the susceptibility of gangliosides to enzymatic degradation

The conformational properties of GM2, GalNacbeta-4(Neu5Acalpha-3) Galbeta-4Glcbeta-1Cer have been compared to those of 6'-GM2, in which the linkage between the GalNAc and Gal was altered from GalNacbeta-4Galbeta- to GalNacbeta-6Galbeta-, and to those of GD1a, Neu5Acalpha-3Galbeta-3GalNAcbeta-4(Neu5Acalpha-3 )Galbeta-4Glcbeta-1Cer, and GalNAc-GD1a. Our results revealed that unlike the compact and rigid oligosaccharide head group found in GM2, where the Neu5Ac and the GalNAc residues interact, the sugar chain of 6'-GM2 is in an open spatial arrangement, with the Neu5Ac no longer interacting with GalNAc, freely accessible to external interactions. The structure of GD1a can be regarded as that of GM2 with an extension of the terminal Neu5Acalpha-3Galbeta-disaccharide. The inner portion of GD1a is that of GM2 comprising the very rigid GalNAc-[Neu5Ac-]Gal trisaccharide. The terminal Neu5Ac-Gal linkage is flexible and fluctuates between two limiting conformations. In GalNAc-GD1a the outer sialic acid gains conformational rigidity due to the presence of the outer GalNAc in position 4 of galactose. This ganglioside has two 'core' GalNAc-[Neu5Ac-]Gal trisaccharide linked in tandem.

Structural basis for the resistance of Tay-Sachs ganglioside GM2 to enzymatic degradation

To understand the reason why, in the absence of GM2 activator protein, the GalNAc and the NeuAc in GM2 (GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer) are refractory to beta-hexosaminidase A and sialidase, respectively, we have recently synthesized a linkage analogue of GM2 named 6'GM2 (GalNAcbeta1-->6(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer). While GM2 has GalNAcbeta1-->4Gal linkage, 6'-GM2 has GalNAcbeta1-->6Gal linkage (Ishida, H., Ito, Y., Tanahashi, E., Li, Y.-T., Kiso, M., and Hasegawa, A. (1997) Carbohydr. Res. 302, 223-227). We have studied the enzymatic susceptibilities of GM2 and 6'GM2, as well as that of the oligosaccharides derived from GM2, asialo-GM2 (GalNAcbeta1-->4Galbeta1--> 4Glcbeta1-1'Cer) and 6'GM2. In addition, the conformational properties of both GM2 and 6'GM2 were analyzed using NMR spectroscopy and molecular mechanics computation. In sharp contrast to GM2, the GalNAc and the Neu5Ac of 6'GM2 were readily hydrolyzed by beta-hexosaminidase A and sialidase, respectively, without GM2 activator. Among the oligosaccharides derived from GM2, asialo-GM2, and 6'GM2, only the oligosaccharide from GM2 was resistant to beta-hexosaminidase A. Conformational analyses revealed that while GM2 has a compact and rigid oligosaccharide head group, 6'GM2 has an open spatial arrangement of the sugar units, with the GalNAc and the Neu5Ac freely accessible to external interactions. These results strongly indicate that the resistance of GM2 to enzymatic hydrolysis is because of the specific rigid conformation of the GM2 oligosaccharide.

Comparison of the frequency-doubled Q-switched Nd:YAG laser and 35% trichloroacetic acid for the treatment of face lentigines

BACKGROUND

Face lentigines are one of the manifestations of photodamaged skin and often put people in socially embarrassing situations. Several lasers have been used to remove lentigines at vast expense. However, trichloroacetic acid (TCA) is an alternative for treating lentigines that costs much less.

OBJECTIVE

To compare the efficacy of the frequency-doubled Q-Switched Nd:YAG laser (532 nm) and 35% TCA for the treatment of face lentigines.

METHODS

Twenty patients (Fitzpatrick skin Types III-IV) with a total of 37 lentigines on faces were randomly collected; each lentigo was divided into medial and lateral halves. Frequency-doubled Q-switched Nd:YAG laser (532 nm) and 35% TCA were applied to the medial and lateral halves of each lentigo respectively. The efficacy after 1 treatment was compared after 6 months.

RESULTS

The frequency-doubled Q-switched Nd:YAG laser (532 nm) had a better result than that of 35% TCA for the treatment of facial lentigines.

CONCLUSION

In order to get a better result after one treatment, the authors suggest the frequency-doubled Q-switched Nd:YAG laser (532 nm) rather than 35% TCA for treating lentigines even though the cost of frequency-doubled Q-switched Nd:YAG laser (532 nm) is greater than that of 35% TCA for both physician and patient.

The 1.8 A structures of leech intramolecular trans-sialidase complexes: evidence of its enzymatic mechanism

Intramolecular trans-sialidase from leech (Macrobdella decora) is the first member of the sialidase superfamily found to exhibit strict specificity towards the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates. Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes an intramolecular trans-sialosyl reaction. Crystal structures of its complexes with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product 2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat conformation of the pyranose observed in the complexes supports the proposed enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively charged C2 of the intermediate. A generalized mechanism is proposed for the sialidase superfamily.

Naturally occurring GM2 gangliosidosis in two Muntjak deer with pathological and biochemical features of human classical Tay-Sachs disease (type B GM2 gangliosidosis)

Two juvenile sibling male Muntjak deer (Muntiacus muntjak) with histories of depression, ataxia, circling and visual deficits were studied. Cerebrospinal fluid analyses revealed vacuolated macrophages that contained long parallel needle-like intracytoplasmic inclusions. Light microscopically, nerve cell bodies throughout the brain, ganglion cells within the retina and neurons in the myenteric plexuses were variably swollen and had pale granular to finely vacuolated eosinophilic cytoplasm. Neuronal cytoplasm stained specifically with sudan black and Luxolfast blue stains. Within the brain there were occasional axonal spheroids, foci of astrogliosis and scattered microglial cells with abundant pale foamy cytoplasm. Electron microscopy of the brain and retina revealed numerous neurons and ganglion cells, respectively, with multiple membrane-bound structures that contained compact electron-dense membranous whorls and fewer parallel membranous stacks. Thin layer chromatography of total lipid extracts of the cerebral cortex of both cases revealed massive accumulation of G(M2) ganglioside. Crude kidney extracts of the two affected deer were able to hydrolyze 4-methylumbelliferyl beta-GlcNAc, but not 4-methylumbelliferyl beta-GlcNAc-6-sulfate, indicating the defect of beta-hexosaminidase A. Cellogel electrophoresis of the kidney extracts also revealed the deficiency of beta-hexosaminidase A in the two deer. It is concluded that these two deer had the biochemical lesion identical to that of human type B G(M2) gangliosidosis (classical Tay-Sachs disease).

Diagnosis and treatment of adrenal tumours: a review of 35 years' experience

OBJECTIVE

To review and analyse clinical data on the diagnosis and management of patients with adrenal masses.

PATIENTS AND METHODS

Patients admitted with adrenal masses between 1960 and 1995 were reviewed. The series comprised 116 males (mean age 41.4 years, SD 10.5, range 3-77) and 95 females (mean 36.9 years, SD 11.6, range 1-62); eight patients were < 14 years old and the overall mean (SD) age was 39.4 (12.8) years. The diagnosis was based on symptoms, signs, hormone levels and imaging studies. All tumours were confirmed by surgery, and pathology and results of analysis assessed statistically.

RESULTS

Over the last 35 years, the incidence of adrenal tumours was 1.7% of all patients admitted with genitourological diseases or 9.7% of patients with genitourinary tumours at our institution. The prevalence of adrenal tumours in males and females was similar but Cushing's syndrome was 3.1 times more frequent in females than in males and phaeochromocytoma 1.9 times more frequent in males than females. Most patients with adrenal tumour were aged 30-50 years. Of 211 adrenal tumours, 151 (72%) were functional, with a prevalence of benign tumour, and 60 (28%) were nonfunctional, with 35% malignant. There were 78 'incidentalomas' which included 18 functional tumours. Overall, 210 tumours were removed and one was explored. Correlation analysis between tumour size and character or hormone levels showed that size was significantly positively correlated with tumour character (r = 0.4010, P < 0.001), but there was no relationship between tumour size and hormonal levels. The postoperative complication rate was 3.3% and the mortality 0.5%.

CONCLUSIONS

Based on this analysis we recommend that computed tomography is the first method used to define and localize the adrenal masses, that hormone levels should be determined in symptomatic or asymptomatic patients with adrenal masses, and that functional adrenal tumours and solid incidentalomas of any size should be removed surgically.

The crystal structure of an intramolecular trans-sialidase with a NeuAc alpha2-->3Gal specificity

BACKGROUND

Intramolecular trans-sialidase from leech (Macrobdella decora) is a unique enzyme which cleaves the terminal neuraminic acid (NeuAc) residue from sialoglycoconjugates, releasing 2, 7-anhydro-neuraminic acid (2,7-anhydro-NeuAc). It is the first enzyme found to exhibit strictly specific cleavage of NeuAc alpha2-->3Gal linkages in sialoglycoconjugates. The release of 2,7-anhydro-NeuAc instead of NeuAc implies a unique mechanism, in which the sialosyl linkage is transferred within the sialoglycoconjugate rather than hydrolyzed. The aims of the structural study were to gain structural insight into the strict specificity and unique mechanism of this unusual enzyme.

RESULTS

. The 2.0 A crystal structure of recombinant leech intramolecular trans-sialidase has been solved by multiple isomorphous replacement. The 1.8 A structure of the enzyme in complex with 2-deoxy-2, 3-didehydro-NeuAc was also solved. The refined model comprising residues 81-769 has a catalytic beta-propeller domain (C), a N-terminal lectin-like domain (II) and an irregular beta-stranded domain (III) inserted into the catalytic domain. The structure reveals several possible carbohydrate-binding features: domain II has a concave face, like that of other sialidases, and there is a suitable surface charge distribution at the domain III-C interface.

CONCLUSIONS

Structural comparisons showed closer evolutionary relationships to bacterial sialidases than to viral neuraminidases. Mainchain and sidechain atoms around Thr593 make the glycerol-binding pocket incapable of accommodating an extended equatorial 6-glycerol group, implying that the 6-glycerol group of the reaction intermediate may occupy an axial position, which is also required by the catalytic mechanism. The steric hindrance introduced by the bulky sidechain of Trp734 above the 2-carboxylate group may explain the lack of water involvement in the cleavage reaction and the substrate specificity.

Antibodies to GT1a ganglioside in patients with Guillain-Barré syndrome

Serum antibodies from 8 (13%) of 62 patients with the acute Guillain-Barré syndrome (GBS) and 1 of 3 patients with the Miller Fisher syndrome (MFS) recognized a minor ganglioside in bovine and human brain trisialoganglioside fractions. The ganglioside antigen migrated between GD1a and GD1b on thin-layer chromatograms. The structure of this ganglioside was established to be GT1a by thin-layer chromatography blotting and mass spectrometry. GT1a a ganglioside was also detected in human and bovine peripheral nerves by thin-layer chromatogram immunostaining. Serum from the GBS patients had IgM, IgG, or IgA antibodies against GT1a detectable by enzyme-linked immunosorbent assay (ELISA). Serum from the MFS patient also had elevated levels of IG against GT1a. None of the sera from 43 patients with other neurological diseases or from 24 healthy controls reacted with GT1a. Sera from 6 of 8 GBS patients with anti-Gt1a antibodies also reacted with GQ1b. There was no difference in the incidence of anti-GT1a immunoglobulins in acute GBS patients with or without oculomotor abnormalities. Levels of anti-GT1a antibodies correlated temporally wit clinical symptoms in GBS patients. Although the incidence of dysphagia was slightly higher in GBS patients with anti-GT1a antibodies than in those without, the number of patients studied may have been too small to detect an association between anti-GT1a antibodies and an a specific clinical variant of GBS. Our data demonstrate that a proportion of GBS patients have antibodies against GT1a ganglioside and suggest that these antibodies may play a role in the pathogenesis of neuropathy in GBS.

Specificity of mouse GM2 activator protein and beta-N-acetylhexosaminidases A and B. Similarities and differences with their human counterparts in the catabolism of GM2

Tay-Sachs disease, an inborn lysosomal disease featuring a buildup of GM2 in the brain, is caused by a deficiency of beta-hexosaminidase A (Hex A) or GM2 activator. Of the two human lysosomal Hex isozymes, only Hex A, not Hex B, cleaves GM2 in the presence of GM2 activator. In contrast, mouse Hex B has been reported to be more active than Hex A in cleaving GM2 (Burg, J., Banerjee, A., Conzelmann, E., and Sandhoff, K. (1983) Hoppe Seyler's Z. Physiol. Chem. 364, 821-829). In two independent studies, mice with the targeted disruption of the Hexa gene did not display the severe buildup of brain GM2 or the concomitant abnormal behavioral manifestations seen in human Tay-Sachs patients. The results of these two studies were suggested to be attributed to the reported GM2 degrading activity of mouse Hex B. To clarify the specificity of mouse Hex A and Hex B and to better understand the observed results of the mouse model of Tay-Sachs disease, we have purified mouse liver Hex A and Hex B and also prepared the recombinant mouse GM2 activator. Contrary to the findings of Burg et al., we found that the specificities of mouse Hex A and Hex B toward the catabolism of GM2 were not different from the corresponding human Hex isozymes. Mouse Hex A, but not Hex B, hydrolyzes GM2 in the presence of GM2 activator, whereas GM2 is refractory to mouse Hex B with or without GM2 activator. Importantly, we found that, in contrast to human GM2 activator, mouse GM2 activator could effectively stimulate the hydrolysis of GA2 by mouse Hex A and to a much lesser extent also by Hex B. These results provide clear evidence on the existence of an alternative pathway for GM2 catabolism in mice by converting GM2 to GA2 and subsequently to lactosylceramide. They also provide the explanation for the lack of excessive GM2 accumulation in the Hexa gene-disrupted mice.

Synthesis of aryl 3'-sulfo-beta-lactosides as fluorogenic and chromogenic substrates for ceramide glycanases

We have previously reported that 4-methylumbelliferyl 6'-O-benzyl-beta-lactoside (2) is a useful substrate for a fluorometric assay of ceramide glycanase (CGase) (L.-X. Wang, N. V. Pavlova, S.-C. Li, Y.-T. Li and Y. C. Lee, Glycoconjugate J., 13 (1996) 359-365). The introduction of a 6-O-benzyl group at the terminal Gal efficiently protected the substrate from its hydrolysis by exo-galactosidase, permitting the assay of CGase in crude biological materials. However, a drawback of this substrate is its low water-solubility and relatively high Km (at a mM level). Introduction of a sulfate group into 4-methylumbelliferyl beta-lactoside (1) led to the formation of 4-methylumbelliferyl 3'-O-sulfo-beta-lactoside (3), which was found to be a more effective substrate than 2. Moreover, the presence of a 3'-O-sulfate group not only increases the water solubility tremendously, but also protects the substrate from cleavage by exo-beta-galactosidase as the 6'-O-benzyl group in 2 does. In addition to the fluorogenic substrate (3), two sulfated chromogenic substrates, N-tetradecanoyl-4-O(3'-sulfo-beta-lactosyl)-3-nitro-L-tyrosine methyl ester (9) and 2-N-(tetradecanoylamino)-4-nitro-phenyl 3'-sulfo-beta-lactoside (12), were synthesized and their suitability for a photometric assay of CGase was evaluated. Substrates 9 and 12, with a long fatty acid chain attached to the aglycon part, have a Km value close to that of the natural substrate GM1 (at a microM level).

Nimodipine ameliorates impaired eyeblink classical conditioning in older rabbits in the long-delay paradigm

Research using the hippocampally dependent short-conditioned stimulus trace conditioning paradigm demonstrated that nimodipine ameliorated learning deficits in older rabbits. Evidence from in vitro and in vivo measures indicated that the site of drug action was hippocampal pyramidal cells. Acquisition occurs in the long (750 ms) delay conditioning paradigm in the absence of the hippocampus. This experiment with 40 older rabbits was undertaken to determine if nimodipine ameliorates impaired acquisition in a conditioning paradigm not dependent on the hippocampus. Fifteen 90-trial sessions of paired conditioning stimuli were presented to 3 groups receiving daily injections of 0, 1, or 5 mg/kg nimodipine. Explicitly unpaired control groups received 0 or 5 mg/kg nimodipine. Acquisition with the 5 mg/kg dose was significantly faster. Existing evidence suggested that nimodipine acted in the hippocampus, but we could not rule out the possibility that the drug also affected conditioning via the cerebellum.

alpha-KDOase activity in oyster and synthesis of alpha- and beta-4-methylumbelliferyl ketosides of 3-deoxy-D-manno-octulosonic acid

Although alpha- and beta-linked 3-deoxy-D-manno-octulosonic acid (KDO) is found in lipopolysaccharides (LPSs) of Gram-negative bacteria, capsular polysaccharides of microorganisms, and plants, very little is known about its degradation. Using both thin-layer chromatography and the periodate-thiobarbituric acid reaction, we found that the hepatopancreas of oyster (Crassostrea virginica) contained an enzyme (alpha-KDOase) capable of releasing alpha-linked KDO from LPSs. To facilitate the studies of alpha-KDOase, we have carried out the synthesis of 4-methylumbelliferyl-alpha-KDO (alpha-KDO-MU) by conjugating the glycosyl chloride of the per-O-acetylated methylester of KDO with methylumbelliferone by the SN2 type reaction and the catalyzed phase-transfer. In both cases, the beta-anomer was obtained as the major product with a yield of about 80%, whereas the yield of alpha-anomer was only about 7%. Attempts to increase the yield of alpha-anomer were not successful. alpha-KDO-MU was used as substrate to follow the purification of alpha-KDOase from oyster hepatopancreas. The pH optimum for oyster alpha-KDOase was determined to be 4.5 using Re-LPS as substrate and 3.0 using alpha-KDO-MU as substrate. The enzyme was found to be stable in the pH range of 3-8. This enzyme released KDO from different LPSs, including Re-LPS from Escherichia coli and Salmonella minnesota, Rd-LPS from S. minnesota, and de-O-acyl-Re-LPS (Kiang, J., Szu, S. C., Wang, L.X., Tang, M., and Lee, Y. C. (1997) Anal. Biochem. 245, 97-101).

Quantitative determination of Orlistat (tetrahydrolipostatin, Ro 18-0647) in human plasma by high-performance liquid chromatography coupled with ion spray tandem mass spectrometry

A rapid, sensitive and specific analytical method was developed and validated to quantify tetrahydrolipostatin (Orlistat, Ro 18-0647) in human plasma in order to provide pharmacokinetic data from clinical trials. This method employs a preliminary plasma protein precipitation step followed by a simple, one-step liquid-liquid extraction procedure to isolate Ro 18-0647 and its pentadeuterated internal standard, Ro 18-0647-d5, from the biological matrix. Reconstituted extracts were analyzed by liquid chromatography/ion spray tandem mass spectrometry (LC/MS/MS) in the selected reaction monitoring (SRM) mode. Chromatography was carried out using a 2 mm i.d. x 50 mm Deltabond Phenyl column. The eluent was acetonitrile-2 mM ammonium acetate (90:10). The retention time of the analyte was 1.2 min and chromatographic run times were less than 1.5 min. No interferences from anticoagulants, collection devices or endogenous constituents of the plasma were observed. The assay has a lower limit of quantitation (LLQ) of 0.20 ng ml-1 in plasma and a lower limit of detection (LLD) of 0.10 ng ml-1 plasma, based on 1 ml aliquots. The capability to detect 0.025 ng ml-1 in plasma has also been demonstrated. The calibration graphs were linear from 0.20 to 10 ng ml-1. The assay was initially validated with a linear range of 0.20-1.0 ng ml-1. This range was later extended and validated to an upper level of quantitation of 10 ng ml-1. Intra- and inter-assay precision studies showed a mean variability of less than 10%. The recovery, inter-assay precision and accuracy of the method were within acceptable bioanalytical standards. The assay has been shown to reliably provide automated, unattended sample analysis for approximately 150 samples per day. In an additional series of tests, Ro 18-0467 was shown to be stable under conditions that might be encountered during the analysis of samples from clinical trials. This LC/MS/MS assay procedure for Ro 18-0647 in human plasma has proven to be robust, sensitive, specific, accurate and reproducible. This method has been used to analyze over 5000 study samples.

Hippocampus in delay eyeblink classical conditioning: essential for nefiracetam amelioration of learning in older rabbits

Rabbits acquire conditioned responses (CRs) normally with bilateral removal of the hippocampus, but alterations of the intact hippocampus can affect the rate of acquisition. The cognition-enhancing drug, nefiracetam ameliorated the acquisition of CRs in older rabbits, protected membrane dysfunction in hippocampal CA1 neurons following oxygen and glucose deprivation, and promoted the release of diverse neurotransmitters, including acetylcholine. Because the septo-hippocampal cholinergic system is demonstrated to be involved in eyeblink conditioning, this experiment was undertaken to explore whether nefiracetam ameliorates conditioning via the hippocampus. Data from 53 rabbits of a mean age of 28 months were tested under two drug conditions (10 or 0 mg/kg nefiracetam) and 4 lesion conditions (bilateral hippocampectomy, bilateral neocortical removal, sham surgery, no surgery). The three groups of nefiracetam-treated rabbits with intact hippocampus acquired CRs more rapidly than the vehicle-treated groups, but rabbits with bilateral hippocampectomy treated with nefiracetam learned like vehicle-treated rabbits. Results suggest that nefiracetam ameliorates learning via the hippocampus. Because of the parallels between conditioning in rabbits with disrupted hippocampal cholinergic systems and conditioning in Alzheimer's disease (AD), these results suggest that nefiracetam may ameliorate conditioning in AD as it ameliorates conditioning in older rabbits.

Structural organization and expression of the gene for the mouse GM2 activator protein

The GM2 activator protein is an essential component for the degradation of GM2 ganglioside by hexosaminidase A in vivo. Mutations in the human gene coding for the GM2 activator protein cause the AB variant of GM2-gangliosidosis, a condition that is clinically indistinguishable from Tay-Sachs disease. To understand better factors affecting the expression of the GM2 activator protein gene (Gm2a) in mouse tissues, we have determined its exon-intron organization and analyzed its promoter region. Gm2a is about 14 kb, has four exons, and the 5' flanking region contains a CAAT box, Sp1 binding sites, AP-1, AP-2 sites, and a pair of IRE sites. A 1.2-kb fragment upstream from the initiation codon was shown to have promoter activity in NIH 3T3 cells. Similarities between the elements present in Gm2a and Hexa promoters might in part explain their similar expression patterns in mouse tissues. The different levels of GM2 activator protein mRNA in liver, kidney, brain, and testis are not owing to the use of different transcription start sites, because a single start site was found 50 bp upstream from the initiation codon in each these tissues. Northern blot analysis demonstrated variation in the GM2 activator protein mRNA expression during mouse development. Gm2a was mapped to Chromosome (Chr) 11, where it co-segregated with Csfgm.

Structural organization and expression of the gene for the mouse GM2 activator protein

The GM2 activator protein is an essential component for the degradation of GM2 ganglioside by hexosaminidase A in vivo. Mutations in the human gene coding for the GM2 activator protein cause the AB variant of GM2-gangliosidosis, a condition that is clinically indistinguishable from Tay-Sachs disease. To understand better factors affecting the expression of the GM2 activator protein gene (Gm2a) in mouse tissues, we have determined its exon-intron organization and analyzed its promoter region.Gm2a is about 14 kb, has four exons, and the 5' flanking region contains a CAAT box, Spl binding sites, AP-1, AP-2 sites, and a pair of IRE sites. A 1.2-kb fragment upstream from the initiation codon was shown to have promoter activity in NIH 3T3 cells. Similarities between the elements present in Gm2a and Hexa promoters might in part explain their similar expression patterns in mouse tissues. The different levels of GM2 activator protein mRNA in liver, kidney, brain, and testis are not owing to the use of different transcription start sites, because a single start site was found 50 bp upstream from the initiation codon in each these tissues. Northern blot analysis demonstrated variation in the GM2 activator protein mRNA expression during mouse development. Gm2a was mapped to Chromosome (Chr) 11, where it co-segregated with Csfgm.

Interaction of GM2 activator protein with glycosphingolipids

GM2 activator protein is a protein cofactor that has been shown to stimulate the enzymatic hydrolysis of both GalNAc and NeuAc from GM2 (Wu, Y. Y., Lockyer, J. M., Sugiyama, E., Pavlova, N.V., Li, Y.-T., and Li, S.-C. (1994) J. Biol. Chem. 269, 16276-16283). To understand the mechanism by which GM2 activator stimulates the hydrolysis of GM2, we examined the interaction of this activator protein with GM2 as well as with other glycosphingolipids by TLC overlay and Sephacryl S-200 gel filtration. The TLC overlay analysis unveiled the binding specificity of GM2 activator, which was not previously revealed. Under the conditions optimal for the activator protein to stimulate the hydrolysis of GM2 by beta-hexosaminidase A, GM2 activator was found to bind avidly to acidic glycosphingolipids, including gangliosides and sulfated glycosphingolipids, but not to neutral glycosphingolipids. The gangliosides devoid of sialic acids, such as asialo-GM1 and asialo-GM2, and the GM2 derivatives whose carboxyl function in the NeuAc had been modified by methyl esterification or reduction, were only very weakly bound to GM2 activator. These results indicate that the negatively charged sugar residue or sulfate group in gangliosides is one of the important sites recognized by GM2 activator. For comparison, we also studied in parallel the complex formation between glycosphingolipids and saposin B, a separate activator protein with broad specificity to stimulate the hydrolysis of various glycosphingolipids. We found that saposin B bound to neutral glycosphingolipids and gangliosides equally well, and there was an exceptionally strong binding to sulfatide. In contrast to previous reports, we found that GM2 activator formed complexes with GM2 and other gangliosides in different proportions depending on the ratio between the activator protein and the ganglioside in the incubation mixture prior to gel filtration. We were not able to detect the specific binding of GM2 activator to GM2 when GM2 was mixed with GM1 or GM3. Thus, the specificity or the mode of action of GM2 activator cannot be simply explained by its interaction with glycosphingolipids based on complex formation. The binding of GM2 activator to a wide variety of negatively charged glycosphingolipids may indicate that this activator protein has functions other than assisting the enzymatic hydrolysis of GM2.

A 1H NMR investigation of the hydrolysis of a synthetic substrate by KDN-sialidase from Crassostrea virginica

The mechanism of hydrolysis of 4-methylumbelliferyl 3-deoxy-D-glycero-alpha-D-galacto-2-nonulopyranosidonic acid (KDN alpha 2MeUmb, 4) by KDN-sialidase isolated from the hepatopancreas of the oyster Crassostrea virginica has been monitored by 1H NMR spectroscopy. The results of these experiments reveal that KDN-sialidase catalyses the hydrolysis of the synthetic substrate KDN alpha 2MeUmb, with initial release of alpha-D-KDN. This is consistent with an overall mechanism for the hydrolysis which proceeds with retention of anomeric configuration. These results agree with earlier NMR studies of other N-acetylneuraminic acid-recognising sialidases from both viral and bacterial sources.

Cloning and expression of sialidase L, a NeuAcalpha2-->3Gal-specific sialidase from the leech, Macrobdella decora

Sialidase L is a NeuAcalpha2-->3Gal linkage-specific sialidase that releases 2,7-anhydro-NeuAc instead of NeuAc from sialoglycoconjugates (Chou, M.-Y., Li, S.-C., Kiso, M., Hasegawa, A., and Li, Y.-T.(1994) J. Biol. Chem. 269, 18821-18826). A 2. 5-kilobase cDNA of sialidase L was cloned by a combination of methods based on polymerase chain reactions. The composite cDNA sequence reveals an open reading frame coding for 762 amino acids, including a putative 28-residue signal peptide at the N terminus that is similar to the signal sequence of the Clostridium septicum sialidase. The result suggests that sialidase L is a secretory enzyme. The coding sequence excluding the putative signal peptide of sialidase L was overexpressed in Escherichia coli. The purified recombinant enzyme was characterized to be as active as the enzyme isolated from the leech. It also possessed the strict NeuAcalpha2-->3Gal linkage specificity and released the unique cleavage product, 2,7-anhydro-NeuAc from sialoglycoconjugates. The deduced amino acid sequence of sialidase L exhibits little similarity with other reported sialidases. However, sialidase L contains a conserved "FRIP region" and four repeating "Asp box" motifs that align well with the corresponding positions of bacterial sialidases. The predicted beta-strand structures near the conserved motifs of sialidase L are similar to those of Salmonella typhimurium sialidase. Several conserved single amino acid residues of bacterial sialidases, including those known to be involved in the active site of Salmonella enzyme, are conserved in the deduced amino acid sequence of sialidase L. This observation suggests that part of the catalytic mechanism of sialidase L may be similar to the ordinary sialidase.

Eyeblink classical conditioning in Alzheimer's disease and cerebrovascular dementia

Eyeblink classical conditioning (EBCC) is severely and consistently impaired in probable Alzheimer's disease (AD), presumably due to normal age related changes in the cerebellum and AD-related hippocampal cholinergic disruption. Less consistent impairment and more variable EBCC performance was predicted in patients with cerebrovascular dementia (CVD) because some CVD patients should have impairment in EBCC when their lesions affect the EBCC circuitry, whereas others with lesions in noncritical regions should have normal EBCC. As predicted, variability in EBCC performance was greater in patients with CVD than in probable AD patients. Acquisition of conditioned responses in the group of CVD patients was better than in the probable AD group. These data show in another sample of normal control subjects and probable AD patients that EBCC has a high sensitivity for probable AD.

A fluorometric assay of ceramide glycanase with 4-methylumbelliferyl beta-D-lactoside derivatives

4-Methylumbelliferyl 6'-O-benzyl-beta-D-lactoside (6'Bn-MU-Lac) and some related compounds were synthesized via different selective reactions including phase-transfer glycosylation. Their suitability as substrates for a fluorometric assay of ceramide glycanase (CGase) was evaluated. Among others, the 6'Bn-MU-Lac, which is resistant to exogalactosidase, was found to be a suitable substrate for routine assay of the CGase activity. For American leech CGase, the K(m) value is 0.232 mM at pH 5.

Characterization of an alternatively spliced GM2 activator protein, GM2A protein. An activator protein which stimulates the enzymatic hydrolysis of N-acetylneuraminic acid, but not N-acetylgalactosamine, from GM2

GM2 activator protein is a protein cofactor which stimulates the enzymatic hydrolysis of both GalNAc and NeuAc from GM2. We have previously isolated two cDNA clones, GM2 activator cDNA and GM2A cDNA, for human GM2 activator protein (Nagarajan, S., Chen, H.-C., Li, S.-C., Li, Y.-T., and Lockyer, J. M. (1992) Biochem. J. 282, 807-813). GM2A mRNA is an RNA alternative splicing product that contains exons 1, 2, 3, and intron 3 of the genomic DNA sequence of GM2 activator protein (Klima, H., Tanaka, A., Schnabel, D., Nakano, T., Schröder, M., Suzuki, K., and Sandhoff, K. (1991) FEBS Lett. 289, 260-264). GM2A cDNA encodes a protein (GM2A protein) containing 1-109 of the 160 amino acids of human GM2 activator protein, plus a tripeptide (VST) encoded by intron 3 at the COOH terminus. Thus, GM2A protein can be regarded as a form (truncated version) of GM2 activator protein. We have expressed GM2A cDNA in Escherichia coli using pT7-7 as the vector. The recombinant GM2A protein was purified to an electrophoretically homogeneous form and was found to stimulate the hydrolysis of NeuAc from GM2 by clostridial sialidase, but not the hydrolysis of GalNAc from GM2 by beta-hexosaminidase A. Like GM2 activator protein, GM2A protein also specifically recognized the terminal GM2 epitope in GalNAc-GD1a and stimulated the hydrolysis of only the external NeuAc from this ganglioside by clostridial sialidase. These results enabled us to discern the enzymatic hydrolyses of GalNAc and NeuAc from the GM2 epitope and established that the NeuAc recognition domain of GM2 activator protein is located within amino acids 1-109. The presence of GM2A mRNA in human tissues and the selective stimulation of NeuAc hydrolysis by GM2A protein indicate that this activator protein may be involved in the catabolism of GM2 through the asialo-GM2 pathway.

Two different sialidases, KDN-sialidase and regular sialidase in the starfish Asterina pectinifera

We have found the coexistence of two different sialidases in the entrails of the starfish Asterina pectinifera: a regular sialidase (RS), which cleaves sialic acid from sialoglycoconjugates, and a KDN-sialidase (KS) which releases the sialic acid analogue KDN (2-keto-3-deoxy-D-glycero-d-galacto-nononic acid) from KDN-containing glycoconjugates that are resistant to RS. The 6700-fold purified KS and 1300-fold purified RS were prepared to study the properties of these two sialidases. KS and RS from Asterina starfish differ in several properties other than glycon specificity, including molecular mass, isoelectric point (pI) and susceptibility to competitive and non-competitive inhibitors. KS has a molecular mass of 31 kDa and a pI of 8.3 while RS has a molecular mass of 128 kDa and a pI of about 4.8. 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (NeuAc2en), but not 2,3-dehydro-2-deoxy-KDN (KDN2en), is a potent competitive inhibitor of RS (Ki approximately 0.007 mM); however, both NeuAc2en and KDN2en are moderate inhibitors of KS (K1 approximately 0.04 mM). Hg2+ is a potent non-competitive inhibitor of RS but not of KS. KS and RS were examined for their ability to hydrolyse KDN- and NeuAc-containing glycoconjugates. KS hydrolyses 4-methyl-umbelliferyl-alpha-KDN (MU-KDN) 20 times faster than 4-methylumbelliferyl-alpha-NeuAc (MU-NeuAc), while RS hydrolyses MU-NeuAc 88 times faster than MU-KDN at the pH optimum of 4.0 KS effectively hydrolyses KDN-GM3 (where GM3 is NeuAc alpha 2 --> 3Gal beta 1 --> 4Glc beta 1-1' Cer, and Cer is ceramide), KDN alpha 2 --> 3lactose, KDN alpha 2 --> 6lactose, KDN alpha 2 --> 6N-acetylgalactosaminitol, KDN alpha 2 --> 6 (KDN alpha 2 --> 3)N-acetylgalactosaminitol and KDN alpha 2 --> 6(GlcNAc beta 1 --> 3) N-acetylgalactosaminitol. However, under the same conditions, these KDN-containing glycoconjugates are refractory to RS. Conversely, GM3, NeuAc alpha 2 --> 3lactose and NeuAc alpha 2 --> 6lactose are effectively hydrolysed by RS but not by KS.

Isolation of three novel cholinergic neuron-specific gangliosides from bovine brain and their in vitro syntheses

In the present study, three extremely minor but novel Chol-1 antigens, termed X1, X2, and X3 have been isolated from bovine brain gangliosides. Based on the results of sialidase degradation, TLC-immunostaining with anti-Chol-1 antibody and fast atom bombardment mass spectrometry, their chemical structures were identified as: III6NeuAc-GgOse4Cer (X1: GM1 alpha) III6NeuAc,II3NeuAc-GgOse4Cer (X2: GD1a alpha) III6NeuAc,II3NeuAc-NeuGc-GgOse4Cer (X3: GT1b alpha) The yields of GM1 alpha, GD1a alpha, and GT1b alpha, were approximately 150, 20, and 10 micrograms, respectively, from 10 g of the bovine brain ganglioside mixture. In conjunction with our previous observations, all gangliosides with anti-Chol-1 reactivity were found to contain a common sialyl alpha 2-6 N-acetylgalactosamine residue, indicating that this unique sialyl linkage is the specific antigenic determinant. We subsequently examined the biosynthesis of the three novel Chol-1 gangliosides using rat liver Golgi fraction as an enzyme source. The results showed that GM1 alpha, GD1a alpha, and GT1b alpha were synthesized from asialo-GM1, GM1a, and GD1b, respectively, by the action of a GalNAc alpha 2-6sialyltransferase.

Isolation and structural characterization of N-acetyl- and N-glycolylneuraminic-acid-containing GalNAc-GD1a isomers, IV4GalNAcIV3Neu5AcII3Neu5GcGgOse4Cer and IV4GalNAcIV3Neu5GcII3Neu5AcGgOse4Cer, from bovine brain

A ganglioside preparation containing two structurally related minor gangliosides (Gg 1 + 2) was isolated from bovine brain ganglioside mixture and characterized. Treatment of 50 g ganglioside mixture with Clostridium perfrigens sialidase, followed by chromatography on DEAE-Sepharose and silica gel columns, yielded 20 mg Gg 1 + 2. By chemical analyses, 1H- and 13C-NMR spectroscopy, enzymic hydrolyses using human beta-hexosaminidase A and clostridial sialidase, and TLC overlay with the conjugated cholera toxin B subunit, the two novel gangliosides Gg 1 and Gg 2 were identified to be: Gg 1, GalNAc-GD1a(Neu5Ac/Neu5Gc), beta-GalNAc-(1-4)-[alpha-Neu5Ac-(2-3)]-beta- Gal-(1-3)-beta-GalNAc-(1-4)-[alpha-Neu5Gc-(2-3)]-beta-Gal-(1-4)-be ta- Glc-(1-1)-Cer; Gg 2, GalNAc-GD1a(Neu5Gc/Neu5Ac), beta-GalNAc-(1-4)-[alpha-Neu5Gc-(2-3)]- beta-Gal-(1-3)-beta-GalNAc-(1-4)-[alpha-Neu5Ac-(2-3)]-beta-Gal-(1- 4)-beta- Glc-(1-1)-Cer. These two gangliosides contain the identical pentasaccharide backbone except that the substitution of the two sialic acids, Neu5Ac and Neu5Gc, are in the reversed position of the external and the internal Gal residues. Our analyses showed that the content of Gg 1 and Gg 2 were approximately 0.12% and 0.08%, respectively, of the total brain ganglioside mixture.

Specific recognition of N-acetylneuraminic acid in the GM2 epitope by human GM2 activator protein

GM2 Activator is a low molecular weight protein cofactor that stimulates the enzymatic conversion of GM2 into GM3 by human beta-hexosaminidase A and also the conversion of GM2 into GA2 by clostridial sialidase (Wu, Y.-Y., Lockyer, J.M., Sugiyama, E., Pavlova, N.V., Li, Y.-T., and Li, S.-C. (1994) J. Biol. Chem. 269, 16276-16283). Among the five known activator proteins for the enzymatic hydrolysis of glycosphingolipids, only GM2 activator is effective in stimulating the hydrolysis of GM2. However, the mechanism of action of GM2 activator is still not well understood. Using a unique disialosylganglioside, GalNAc-GD1a, as the substrate, we were able to show that in the presence of GM2 activator, GalNAc-GD1a was specifically converted into GalNAc-GM1a by clostridial sialidase, while in the presence of saposin B, a nonspecific activator protein, GalNAc-GD1a was converted into both GalNAc-GM1a and GalNAc-GM1b. Individual products generated from GalNAc-GD1a by clostridial sialidase were identified by thin layer chromatography, negative secondary ion mass spectrometry, and immunostaining with a monoclonal IgM that recognizes the GM2 epitope. Our results clearly show that GM2 activator recognizes the GM2 epitope in GalNAc-GD1a. Thus, GM2 activator may interact with the trisaccharide structure of the GM2 epitope and render the GalNAc and NeuAc residues accessible to beta-hexosaminidase A and sialidase, respectively.

Enzymatic sialylation of N-linked oligosaccharides using an alpha-(2,3)-specific trans-sialidase from Trypanosoma cruzi: structural identification using a three-dimensional elution mapping technique

alpha-(2,3)-Sialylated biantennary and triantennary oligosaccharides were enzymatically prepared from pyridyl-2-amino-oligosaccharides with terminal Gal residues, using an alpha-(2,3)-specific trans-sialidase from Trypanosoma cruzi (Lee, K. B., and Lee, Y. C. (1994) Anal. Biochem. 216, 358-364). From the pyridyl-2-amino-derivatives of neutral and alpha-(2,6)-monosialylated biantennary oligosaccharides from human fibrinogen, 5 different sialyl biantennary oligosaccharides were obtained. From two different asialo-triantennary oligosaccharides from fetuin, 35 sialyl oligosaccharides were obtained. The trans-sialidase transferred sialic acids effectively and indiscriminately to different galactosyl residues in the different positions on the substrates. Since the starting materials are neutral oligosaccharide of established structure, and the only alpha-(2,3)-sialyl residues are added to the nonreducing Gal terminal residues, the structures of these oligosaccharides could be identified unambiguously by using the three-dimensional mapping technique (Takahashi, N., Nakagawa, H., Fujikawa, K., Kawamura, Y., and Tomiya, N. (1995) Anal. Biochem. 226, 139-146.) in combinations with strategic digestion with beta-galactosidase, beta-N-hexosaminidase, and sialidase L.

The glycan keratan sulfate in inner ear crystals

The otoconial matrix (OM) of chicks (Gallus domesticus) inner ear was analyzed. Histochemically the OM was reacted with phosphotungstic acid (PTA) and immunohistochemically with the monoclonal antibody antikeratan sulfate (antiKS). The OM was digested with the enzyme endo-beta-galactosidase (E beta Galase) or separated by 1D and 2D gel electrophoresis. PTA which reacts with glycoproteins precipitated the OM, suggesting that the OM contains glycoproteins. A central core in each crystal had no PTA staining, suggesting that the core lacked glycoproteins. Anti KS antibody stained the OM with increased density in older embryos as determined by color thresholding. E beta Galase, which cleaves the lactosamine repeating units in KS, decreased the immunostain by 30% in the OM and by 20% in the cartilage. The OM from the utricle, saccule and macula lagena contained similar molecular weight bands. Five dense bands in the OM were less dense in tissue and blood controls, suggesting that such bands are enriched in the OM. Isoelectric focusing of the OM showed a negatively charged high molecular weight smear not present in blood and faint in tissue controls. The high affinity of the OM for the cationic PTA stain, the strong immunohistochemical reaction of the OM with anti KS antibody and high molecular weight negative smear in 2D gels taken together suggest that: a) the OM contains large amounts of glycoproteins and glycans, one of which is keratan sulfate, because its immuno stain with antiKS antibody was decreased by the enzyme E beta Galase, b) the utricle, saccule and macula lagena may have similar composition, and c) the concentration of KS may increase gradually until complete mineralization of the OM is reached.

Effect of protein and starch degradation rates on rumen metabolism in Taiwan native goat

Six ruminal and duodenal cannulated Taiwan native goats (body weight = 20 kg) were fed 35% roughage, 65% concentrate diet (crude protein = 9.5%) in a 6 x 6 Latin square design to study the effect of the combination of 3 varying starch (corn) and 2 varying protein (soybeans) ruminal degradation rates on ruminal microbial density and ruminal nutrient digestibilities. Goats in treatment consisting of both rapid starch and protein ruminal degradation rates had higher total bacterial and protozoal numbers than did those in other treatments (p < 0.05). The combination of rapid starch degradation rate and slow protein degradation rate supported the highest numbers of Holotrichs whereas the combination of both rapid starch and protein degradation rate supported the highest numbers of Entodiniomorphs. Ruminal starch digestibilities were higher for treatment diets with autoclaved corn than for those with raw corn whereas ruminal digestibility of protein was greater in diets with raw soybeans than in those with heated ones. Higher neutral detergent fiber digestibilities in the rumen were found with the raw corn rations and the raw soybean rations.

Detection of noncovalent FKBP-FK506 and FKBP-Rapamycin complexes by capillary electrophoresis-mass spectrometry and capillary electrophoresis-tandem mass spectrometry

The well known biospecific noncovalent receptor-ligand association complexes between the immunophilin FKBP and the immunosuppressive drugs FK506 and Rapamycin (RM) were investigated by on-line capillary electrophoresis-mass spectrometry (CE-MS) under selected ion monitoring (SIM) conditions and by CE-MS with tandem mass spectrometry (CE-MS/MS) under selected reaction monitoring (SRM) conditions. Solutions of hFKBP (33.3 µM) were dissolved in 50 mM ammonium acetate at pH 7.5. Samples that contained 100 µM of FK506 or RM also were prepared under the same solution conditions. By using these aqueous pH neutral conditions, samples were analyzed by SIM CE-MS and SRM CE-MS and the target complexes were separated by CE with mass spectrometer detection of the individual complexes between FKBP and FK506 [hFKBP + FK506 + 7HJ(7+) as well as FKBP and RM [hFKBP + RM + 7HJ(7+). In an experiment where a mixture of FK506 and RM was analyzed in the presence of FKBP, a nine-to-one ratio of ion current abundances between the RM and FK506 complexes was observed as reported in the literature from other studies. These results suggest that CE-MS and CE-MS/MS may be yet another analytical method for studying noncovalent interactions of biologically important macromolecules under physiological conditions.

Characterization of a deaminated neuraminic acid-containing glycoprotein from the skin mucus of the loach, Misgurnus anguillicaudatus

Using NMR spectroscopy and mass spectrometry, the major sialic acid of the skin mucus of the loach, Misgurnus anguillicaudatus was found to be 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN). We have subsequently devised a method to isolate a KDN-containing glycoprotein preparation from loach skin mucus. The method involves the sonication of the skin mucus with 0.05 M Tris-HCl, pH 8.0, to solubilize the glycoprotein, followed by DE52-cellulose chromatography of the extract, Nuclease P1 treatment, and Sepharose CL-4B gel filtration. The purified glycoprotein preparation was found to contain 38.5% KDN, 0.4% NeuAc, 24.6% GalNAc, 3.3% Gal, and 28.2% amino acids (w/w). The amino acid composition of this glycoprotein preparation revealed that it is unusually rich in Thr, and 6 amino acids, Thr, Ser, Glu (or Gln), Pro, Gly and Ala, account for 83% of the total amino acids. This glycoprotein is extremely poor in Cys, Met, Tyr, Phe, Arg, and Trp. Treatment of this glycoprotein with alkali resulted in the destruction of 83% of Thr suggesting that most of the sugar chains in this glycoprotein are linked through Thr. Alkaline borohydride treatment of 100 mg of the glycoprotein preparation, followed by Sephadex G-25 (superfine) gel filtration, yielded two major oligosaccharide alditols, I (15.4 mg) and II (15.6 mg). Using liquid secondary ion mass spectrometry and methylation analysis, I was identified to be KDN alpha 2-->6GalNAc-ol and II, KDN alpha 2-->6(KDN alpha 2-->3)-GalNAc-o1. KDN alpha 2-->6GalNAc is structurally similar to NeuAc alpha 2-->GalNAc found in ovine submaxillary glycoprotein while II represents a novel structure which contains two sialic acids linked to a GalNAc through both alpha 2-->3 and alpha 2-->6 linkages. This structure has never been found in mucin type glycoproteins including mammalian epithelial mucin glycoproteins. This is the first report of the presence of a mucin type glycoprotein which contains KDN instead of NeuAc or NeuGc in fish skin mucus.

Nicotinic cholinergic system involvement in eyeblink classical conditioning in rabbits

A nicotinic cholinergic antagonist, mecamylamine (MEC), was administered to rabbits tested on eyeblink classical conditioning (EBCC) in the 750-ms delay paradigm for 10 90-trial sessions. Nicotinic receptors were measured in 3 brain regions in 5 treatment groups: paired conditioned stimulus-unconditioned stimulus (CS-US) presentations with (a) vehicle, young; (b) vehicle, older; (c) 0.5 mg/kg MEC, young; unpaired CS-US with (d) 0.5 mg/kg MEC, young; and (e) vehicle, young. Daily MEC injections disrupted acquisition in young rabbits (769 trials to learning criterion vs. 323 trials for vehicle-treated young rabbits). MEC-treated young rabbits learned similarly to older rabbits. Brain nicotinic receptors were not affected by 10 daily MEC injections. To our knowledge, this experimental protocol, using a low MEC dose to selectively inhibit nicotinic cholinergic receptors, is the first to demonstrate a role for nicotinic cholinergic receptors in EBCC.

Biosynthetic pathway for a new series of gangliosides, GT1a alpha and GQ1b alpha

A new class of gangliosides, GT1a alpha and GQ1b alpha, were initially identified as cholinergic neuron-specific antigens in bovine brain. These gangliosides have in common alpha 2-6 NeuAc linked to the GalNAc residue in the gangliotetraose core structure. In this study, we have determined the biosynthetic pathways of GT1a alpha and GQ1b alpha using rat liver Golgi fraction. The results showed that GT1a alpha and GQ1b alpha were synthesized from GD1a and GT1b, respectively, by the action of a GalNAc alpha 2-6 sialyltransferase. It was also demonstrated that these two gangliosides were found to exist as extremely minor components in rat liver.

Purification and characterization of sialidase L, a NeuAc alpha 2-->3Gal-specific sialidase

Sialidase L releases 2,7-anhydro-NeuAc from sialoglycoconjugates (Li, Y.-T., Nakagawa, H., Ross, S. A., Hansson, G., and Li, S.-C. (1990) J. Biol. Chem. 265, 21629-21633). This enzyme has been purified more than 10,000-fold from Macrobdella leech. The final preparation gives a single protein band on SDS-polyacrylamide gel electrophoresis with the molecular mass of 84 kDa. The pI is determined to be 6.0 using isoelectric focusing. With 4-methylumbelliferyl-alpha-NeuAc as substrate, the pH optimum is between pH 5.5-7.0. Unlike regular sialidases, sialidase L is not inhibited by 2-deoxy-2,3-dehydro-NeuAc. Two of the seven tryptic peptides derived from sialidase L contain the consensus repeat S-X-D-X-G-X-T-W that has been found in the regular sialidases. Among various sialoglycoconjugates tested, sialidase L cleaves only the NeuAc alpha 2-->3Gal linkage. NeuAc alpha 2-->6Gal, NeuAc alpha 2-->6GalNAc, NeuAc alpha 2-->6GlcNAc, NeuAc alpha 2-->8-NeuAc, and NeuAc alpha 2-->9NeuAc linkages are not hydrolyzed. At pH 7.0, sialidase L and Clostridial sialidase release 46 and 92% of sialic acid, respectively, from bovine fetuin, indicating that sialidase L selectively cleaves NeuAc alpha 2-->3Gal linkages in fetuin. Sialidase L is the first sialidase found to exhibit a strict specificity toward the hydrolysis of the NeuAc alpha 2-->3Gal linkage, and it should become useful for the selective cleavage of NeuAc alpha 2-->3Gal linkages in sialoglycoconjugates without destroying other sialosyl linkages.

Expression and specificity of human GM2 activator protein

The cDNA encoding GM2 activator was expressed in the Escherichia coli/pT7-7 system. The yield of the GM2 activator with greater than 99% purity was about 3 mg per liter culture. The recombinant GM2 activator was found to be as active as that isolated from human kidney. The availability of the recombinant GM2 activator enabled us to critically examine the specificity of this activator protein. Our results show that the specificity of GM2 activator is not as strict as that reported previously. Although GM2 activator stimulates most efficiently the degradation of GM2 carried out by beta-N-acetylhexosaminidase A (Hex A), this activator also stimulates the following reactions: (a) conversion of GM2 to GA2 by clostridial sialidase; (b) hydrolysis of GalNAc from dipalmitoylphosphatidylethanolamine-II3NeuAcGgOse3 by Hex A; and (c) liberation of Gal from GM1 by beta-galactosidase at a high activator concentration. Thus, this activator does not differentiate between GM2 and dipalmitoylphosphatidylethanolamine-II3NeuAcGgOse3 or between Hex A and clostridial sialidase. The micellar forms of GD2 and GalNAc-GD1a were found to be more readily hydrolyzed by Hex A than GM2 in the absence of GM2 activator. Our results also show that saposin B can enhance the stimulatory activity of GM2 activator, but it cannot promote the stimulatory activity of sodium taurodeoxycholate. Taken together, our results suggest that the mechanism of action of GM2 activator is different from saposin B, and the action of GM2 activator is more than to solubilize lipid substrates. The effectiveness of GM2 activator in stimulating the hydrolysis of GM2 may be due to its ability to recognize the specific trisaccharide structure of the GM2 epitope, GalNAc beta 1-->4(NeuAc alpha 2-->3)Gal-, and to modify the GalNAc-NeuAc interaction in this structure.

Nicotinic cholinergic system involvement in eyeblink classical conditioning in rabbits

A nicotinic cholinergic antagonist, mecamylamine (MEC), was administered to rabbits tested on eyeblink classical conditioning (EBCC) in the 750-ms delay paradigm for 10 90-trial sessions. Nicotinic receptors were measured in 3 brain regions in 5 treatment groups: paired conditioned stimulus-unconditioned stimulus (CS-US) presentations with (a) vehicle, young; (b) vehicle, older; (c) 0.5 mg/kg MEC, young; unpaired CS-US with (d) 0.5 mg/kg MEC, young; and (e) vehicle, young. Daily MEC injections disrupted acquisition in young rabbits (769 trials to learning criterion vs. 323 trials for vehicle-treated young rabbits). MEC-treated young rabbits learned similarly to older rabbits. Brain nicotinic receptors were not affected by 10 daily MEC injections. To our knowledge, this experimental protocol, using a low MEC dose to selectively inhibit nicotinic cholinergic receptors, is the first to demonstrate a role for nicotinic cholinergic receptors in EBCC.

A nicotinic agonist (GTS-21), eyeblink classical conditioning, and nicotinic receptor binding in rabbit brain

The septo-hippocampal cholinergic system is of demonstrated involvement in eyeblink classical conditioning (EBCC). To determine if a nicotinic cholinergic agonist, GTS-21, would facilitate acquisition of EBCC in older rabbits, three doses (0.1, 0.5, 1.0 mg/kg) in sterile saline vehicle and vehicle alone were administered to older rabbits (n = 48; mean age = 29.8 months). A control group of vehicle-treated young rabbits (n = 12; mean age = 3.5 months) was included. Rabbits were conditioned for fifteen 90-trial sessions in the 750 ms delay paradigm with a tone conditioned stimulus and corneal airpuff unconditioned stimulus. Dependent measures of trials to learning criterion, percentage of conditioned responses (CRs) and CR amplitude consistently showed significant improvement in older rabbits treated with 0.5 and 1.0 mg/kg of GTS-21. Acquisition was similar in vehicle-treated young and GTS-treated older rabbits. Vehicle-treated older rabbits conditioned more poorly than vehicle-treated young rabbits. No non-associative learning effects were observed in GTS-21 treated animals. Nicotinic receptor binding was similar in all groups of older rabbits, indicating that GTS-21 administration over a 15-day period did not affect nicotinic receptors. Alzheimer's disease (AD) has been associated with significant loss of nicotinic cholinergic receptors, and patients diagnosed with probable AD are seriously impaired on EBCC. These results demonstrating that the nicotinic agonist, GTS-21, facilitated EBCC in older rabbits suggest that the compound should receive additional investigation for its potential to affect cognition in AD.