Structural but Not Functional Alterations in Cones in the Absence of the Retinal Disease Protein Retinitis Pigmentosa 2 (RP2) in a Cone-Only Retina

X-linked retinitis pigmentosa 2 (XLRP2) patients and Rp2 ^null mice exhibit severe cone photoreceptor degeneration. However, due to the paucity of cones in mammalian model systems, it is not clear how cones respond to the loss of RP2. Here we have used the Nrl^-/- mice, which develop a rodless and short wavelength (S) opsin-containing cone-only retina, to generate Rp2 ^null::Nrl^-/- double knock out (Rp2-DKO) mice. We found that the ciliary axoneme and the outer segments (OSs) of the cones were significantly longer with disorganized membrane infoldings as compared to the Nrl^-/- mice. Additionally, we found misregulation in the expression of the genes related to ophthalmic disease, cell trafficking, and stress-response in the Rp2-DKO mice prior to the onset of cone degeneration. Surprisingly, the loss of RP2 did not affect progressive photoreceptor dysfunction of the Nrl^-/- mice and the trafficking of S opsin. Our data suggest that RP2 is a negative regulator of cone OS length but does not affect S-opsin trafficking and S-cone function. Our studies also provide a cone-only platform to design cone-targeted therapeutic strategies for X-linked RP2.

Prenylated retinal ciliopathy protein RPGR interacts with PDE6δ and regulates ciliary localization of Joubert syndrome-associated protein INPP5E

Ciliary trafficking defects underlie the pathogenesis of severe human ciliopathies, including Joubert Syndrome (JBTS), Bardet-Biedl Syndrome, and some forms of retinitis pigmentosa (RP). Mutations in the ciliary protein RPGR (retinitis pigmentosa GTPase regulator) are common causes of RP-associated photoreceptor degeneration worldwide. While previous work has suggested that the localization of RPGR to cilia is critical to its functions, the mechanism by which RPGR and its associated cargo are trafficked to the cilia is unclear. Using proteomic and biochemical approaches, we show that RPGR interacts with two JBTS-associated ciliary proteins: PDE6δ (delta subunit of phosphodiesterase; a prenyl-binding protein) and INPP5E (inositol polyphosphate-5-phosphatase 5E). We find that PDE6δ binds selectively to the C-terminus of RPGR and that this interaction is critical for RPGR’s localization to cilia. Furthermore, we show that INPP5E associates with the N-terminus of RPGR and trafficking of INPP5E to cilia is dependent upon the ciliary localization of RPGR. These results implicate prenylation of RPGR as a critical modification for its localization to cilia and, in turn suggest that trafficking of INPP5E to cilia depends upon the interaction of RPGR with PDE6δ. Finally, our results implicate INPP5E, a novel RPGR-interacting protein, in the pathogenesis of RPGR-associated ciliopathies.

The carboxyl terminal mutational hotspot of the ciliary disease protein RPGRORF15 (retinitis pigmentosa GTPase regulator) is glutamylated in vivo

Mutations in RPGR^ORF15 (retinitis pigmentosa GTPase regulator) are a major cause of inherited retinal degenerative diseases. RPGR^ORF15 (1152 residues) is a ciliary protein involved in regulating the composition and function of photoreceptor cilia. The mutational hotspot in RPGR^ORF15 is an unusual C-terminal domain encoded by exon ORF15, which is rich in polyglutamates and glycine residues (Glu-Gly domain) followed by a short stretch of basic amino acid residues (RPGR^C2 domain; residues 1072-1152). However, the properties of the ORF15-encoded domain and its involvement in the pathogenesis of the disease are unclear. Here we show that RPGR^ORF15 is glutamylated at the C-terminus, as determined by binding to GT335, which recognizes glutamylated substrates. This reactivity is lost in two mouse mutants of Rpgr, which do not express RPGR^ORF15 due to disease-causing mutations in exon ORF15. Our results indicate that RPGR^ORF15 is posttranslationally glutamylated in the Glu-Gly domain and that the GT335 antibody predominantly recognizes RPGR^ORF15 in photoreceptor cilia.

Summary: This study shows that the mutational hotspot of ciliary protein RPGR^ORF15, commonly associated with severe blindness, is posttranslationally glutamylated at its C-terminus and is a target of GT335.

Ciliopathy-associated protein CEP290 modifies the severity of retinal degeneration due to loss of RPGR

Mutations in RPGR (retinitis pigmentosa GTPase regulator) are the most common cause of X-linked RP, a severe blindness disorder. RPGR mutations result in clinically variable disease with early- to late-onset phenotypic presentation. Molecular mechanisms underlying such heterogeneity are unclear. Here we show that phenotypic expression of Rpgr-loss in mice is influenced genetically by the loss of Cep290, a human ciliopathy gene. We found that Rpgr^ko/Y mice with a heterozygous hypomorphic allele of Cep290 (Cep290^rd16/+) but not of a heterozygous null allele of Cep290 (Cep290^null/+) or of other ciliopathy genes, Rpgrip1, Nphp1, Nphp4 and Nphp5, exhibit relatively early onset (by 3 months of age) retinal degeneration and dysfunction when compared with the onset at ∼7 months of age in the Rpgr^ko/Y mice. We also observed disorganized photoreceptor outer-segment morphology and defective trafficking of opsins in the Rpgr^ko/Y::Cep290^rd16/+ mice. Together with a physical interaction between RPGR and the C-terminal domain of CEP290, our data suggest that RPGR and CEP290 genetically interact and highlight the involvement of hypomorphic alleles of genes as potential modifiers of heterogeneous retinal ciliopathies.

Loss of human disease protein retinitis pigmentosa GTPase regulator (RPGR) differentially affects rod or cone-enriched retina

It is unclear how genes, such as RPGR (retinitis pigmentosa guanine triphosphatase regulator) that are expressed in both rods and cones, cause variable disease pathogenesis. Using transcriptomic analysis, we show that loss of RPGR in a rod-dominant mouse retina (Rpgr(ko)) results in predominant alterations in genes involved in actin cytoskeletal dynamics, prior to onset of degeneration. We validated these findings and found an increase in activated RhoA-GTP levels and polymerized F-actin in the Rpgr(ko) mouse retina. To assess the effect of the loss of RPGR in the all-cone region of the human retina, we used Nrl(-/-) (neural retina leucine zipper) mice, to generate Rpgr(ko)::Nrl(-/-) double-knock-out (Rpgr-DKO) mice. These mice exhibited supranormal cone response to light and substantially retained retinal architecture. Transcriptomic analysis revealed predominant up-regulation of retinal pigmented epithelium (RPE)-specific genes associated with visual cycle, whereas fatty acid analysis showed mild decrease in docosahexaenoic acid in the retina of the Rpgr-DKO mice when compared with the Nrl(-/-) mice. Our data reveal new insights into distinct intracellular pathways that are involved in RPGR-associated rod and cone dysfunction and provide a platform to design new treatment modalities.

Biocompatible and Antibacterial SnO2 Nanowire Films Synthesized by E-Beam Evaporation Method

In this work, the biocompatibility and antibacterial activities of novel SnO2 nanowire coatings prepared by electron-beam (E-Beam) evaporation process at low temperatures were studied. The nanowire coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) methods. The results of in vitro cytotoxicity and cell proliferation assays suggested that the SnO2 nanowire coatings were nontoxic and promoted the proliferation of C2C12 and L929 cells (> 90% viability). Cellular activities, cell adhesion, and lactate dehydrogenase activities were consistent with the superior biocompatibility of the nanowire materials. Notably, the nanowire coating showed potent antibacterial activity against six different bacterial strains. The antibacterial activity of the SnO2 material was attributed to the photocatalytic nature of SnO2. The antibacterial activity and biocompatibility of the newly developed SnO2 nanowire coatings may enable their use as coating materials for biomedical implants.

Ablation of retinal ciliopathy protein RPGR results in altered photoreceptor ciliary composition

Cilia regulate several developmental and homeostatic pathways that are critical to survival. Sensory cilia of photoreceptors regulate phototransduction cascade for visual processing. Mutations in the ciliary protein RPGR (retinitis pigmentosa GTPase regulator) are a prominent cause of severe blindness disorders due to degeneration of mature photoreceptors. However, precise function of RPGR is still unclear. Here we studied the involvement of RPGR in ciliary trafficking by analyzing the composition of photoreceptor sensory cilia (PSC) in Rpgr^ko retina. Using tandem mass spectrometry analysis followed by immunoblotting, we detected few alterations in levels of proteins involved in proteasomal function and vesicular trafficking in Rpgr^ko PSC, prior to onset of degeneration. We also found alterations in the levels of high molecular weight soluble proteins in Rpgr^ko PSC. Our data indicate RPGR regulates entry or retention of soluble proteins in photoreceptor cilia but spares the trafficking of key structural and phototransduction-associated proteins. Given a frequent occurrence of RPGR mutations in severe photoreceptor degeneration due to ciliary disorders, our results provide insights into pathways resulting in altered mature cilia function in ciliopathies.

Complex genetic mechanisms in glaucoma: an overview

Glaucomas comprise a group of hereditary optic neuropathies characterized by progressive and irreversible visual field loss and damage to the optic nerve head. It is a complex disease with multiple molecular mechanisms underlying its pathogenesis. Genetic heterogeneity is the hallmark of all glaucomas and multiple chromosomal loci have been linked to the disease, but only a few genes have been characterized, viz. myocilin (MYOC), optineurin (OPTN), WDR36 and neurotrophin-4 (NTF4) in primary open angle glaucoma (POAG) and CYP1B1 and LTBP2 in congenital and developmental glaucomas. Case-control-based association studies on candidate genes involved in different stages of glaucoma pathophysiology have indicated a very limited involvement. The complex mechanisms leading to glaucoma pathogenesis indicate that it could be attributed to multiple genes with varying magnitudes of effect. In this review, we provide an appraisal of the various efforts in unraveling the molecular mystery in glaucoma and also some future directions based on the available scientific knowledge and technological developments.

Variations in NTF4, VAV2, and VAV3 genes are not involved with primary open-angle and primary angle-closure glaucomas in an indian population

PURPOSE

Recently, the neurotrophin-4 (NTF4), VAV2 and VAV3 genes have been implicated in primary open-angle glaucoma (POAG) in the European and Japanese populations, respectively. This study was conducted to determine their involvement in an Indian population with POAG and primary angle-closure glaucoma (PACG).

METHODS

The entire NTF4 gene and the POAG-associated SNPs rs2156323 (VAV2) and rs2801219 (VAV3) and their flanking regions were screened by resequencing in a clinically well-characterized cohort of 537 subjects that included cases of POAG (n = 141), PACG (n = 111), and ethnically matched normal controls (n = 285). The data were analyzed by using appropriate statistical software.

RESULTS

Resequencing of NTF4 revealed a nonsynonymous (A88V), silent (P151P) and two changes in the 3'UTR region, along with a known polymorphism (rs11669977) in cases of POAG; the PACG cases exhibited only the A88V variation. Of interest, the A88V mutation observed in Europeans was more prevalent in our normal control subjects (4.91%, 95% CI, 2.95-8.07) than in the POAG (2.14%, 95% CI, 0.73-6.11; P = 0.200) and PACG (2.85%, 95% CI, 0.97-8.06; P = 0.577) cases. There were no major differences in the presenting intraocular pressure, cup-to-disc ratio, and visual field defects among patients harboring the A88V variation. The other variations in NTF4 were not associated with the cases. The risk alleles of rs2156323 and rs2801219 in the Japanese were not associated with POAG (P = 0.533 and 0.133, respectively) and PACG (P = 0.223 and 0.394, respectively) in the Indian cohort.

CONCLUSIONS

The present data indicate a lack of involvement of variations in NTF4, VAV2, and VAV3 with glaucoma pathogenesis in an Indian population.

Bowman–Birk protease inhibitor from the seeds of Vigna unguiculata forms a highly stable dimeric structure

Different protease inhibitors including Bowman-Birk type (BBI) have been reported from the seeds of Vigna unguiculata. Protease isoinhibitors of double-headed Bowman-Birk type from the seeds of Vigna unguiculata have been purified and characterized. The BBI from Vigna unguiculata (Vu-BBI) has been found to undergo self-association to form very stable dimers and more complex oligomers, by size-exclusion chromatography and SDS-PAGE in the presence of urea. Many BBIs have been reported to undergo self-association to form homodimers or more complex oligomers in solution. Only one dimeric crystal structure of a BBI (pea-BBI) is reported to date. We report the three-dimensional structure of a Vu-BBI determined at 2.5 A resolution. Although, the inhibitor has a monomer fold similar to that found in other known structures of Bowman-Birk protease inhibitors, its quaternary structure is different from that commonly observed in this family. The structural elements responsible for the stability of monomer molecule and dimeric association are discussed. The Vu-BBI may use dimeric or higher quaternary association to maintain the physiological state and to execute its biological function.

Ethnobotanical survey of plants used to treat asthma in Andhra Pradesh, India

Tribal and non-tribal inhabitants of Andhra Pradesh used nearly 80 medicinal plants for treating asthma. The tribal people have a strong faith and belief in the traditional health care system, through herbal treatment. Plant species are generally used along with other materials and plant products in different combinations to effective cure. Herbalists reported that plant ingredients are used in the form of dry powder, decoction and juice in the treatment of asthma. The knowledge of most asthma drug plants used in herbal treatment and their method of using them are confined to some of the local healers. Some of the plants mentioned by local healers however, are extensively used nationally in the preparation of Ayurvedic medicines including those to treat asthma. Clinical and pharmacological data are available for these plants. Most of the plants used for treating asthma by local herbalists appear not to have been recorded hitherto.

Two orthorhombic crystal structures of a galactose-specific lectin from Artocarpus hirsuta in complex with methyl-alpha-D-galactose

Based on their carbohydrate specificity, the jacalin family of lectins can be divided into two groups: galactose-specific and mannose-specific. The former are cytoplasmic proteins, whereas the latter are localized in the storage vacuoles of cells. It has been proposed that the post-translational modification in some of the lectins that splits their polypeptide chains into two may be crucial for galactose specificity. The mannose-specific members of the family are single-chain proteins that lack the above modification. Although the galactose-specific and the mannose-specific jacalin-type lectins differ in their sequences, they share a common fold: the beta-prism I fold, which is characteristic of Moraceae plant lectins. Here, two crystal structures of a jacalin-related lectin from Artocarpus hirsuta, which is specific for galactose, in complex with methyl-alpha-D-galactose are reported. The lectin crystallized in two orthorhombic forms and one hexagonal form under similar conditions. The crystals had an unusually high solvent content. The structure was solved using the molecular-replacement method using the jacalin structure as a search model. The two orthorhombic forms were refined using data to 2.5 and 3.0 A resolution, respectively. The structures of the A. hirsuta lectin and jacalin are identical. In orthorhombic form I the crystal packing provides three different micro-environments for sugar binding in the same crystal. The observed difference in the specificity for oligosaccharides between the A. hirsuta lectin and jacalin could only be explained based on differences in the molecular associations in the packing and variation of the C-terminal length of the beta-chain. The observed insecticidal activity of A. hirsuta lectin may arise from its similar fold to domain II of the unrelated delta-endotoxin from Bacillus thuringiensis.

Phenytoin decreases the blood concentrations of sirolimus in a liver transplant recipient: a case report

This report documents that coadministration of phenytoin leads to decreased blood concentrations and area under the blood concentration-time curve of sirolimus in a liver transplant patient. It is essential to monitor the blood concentrations of sirolimus and adjust the sirolimus dosage when phenytoin administration begins or ends.

Interaction-induced enhancement in the activity and selectivity of a titania-supported ammonium salt of a 12-molybdophosphoric acid catalyst during ammoxidation of 2-methylpyrazine

A titania-supported ammonium salt of 12-molybdophosphoric acid has been synthesized, and the salt-support interaction, which enhanced the reaction rate, has been correlated with the activity of the catalyst in the ammoxidation of 2-methylpyrazine.

Nutritional neglect and physical abuse in children of alcoholics

OBJECTIVE

Children of alcoholics are at higher risk for physical injuries and malnutrition. In this study nutritional neglect and physical abuse in children of alcoholics has been compared with children of non-alcoholics in a General Hospital attached to a Medical College.

METHODS

72 children of alcoholics were compared with 81 normal controls. 86.1% in case group and 49.4% in control group had malnourishment of various grades.

RESULTS

45% of the children of alcoholics had physical injuries in contrast to 23.4% of children of non-alcoholics. Malnutrition co-existed in almost all injured children of alcoholics.

CONCLUSION

Alcoholism in parents of malnourished and injured children are frequently ignored in routine clinical evaluation. If the risk children are identified early some of the morbidity can be avoided.

Changes in serum and hepatic cholesterol in lead-induced liver hyperplasia

Lead nitrate when injected intravenously as a single dose to male Wistar rats causes a strong hepatic proliferative response followed by reabsorption of excess tissue within 10-14 days. The rate of cell proliferation in this hyperplastic model was positively correlated with hepatic de novo synthesis of cholesterol, stimulation of the hexose monophosphate shunt pathway of glucose metabolism and with alterations in serum lipoproteins.

Value of measurement of hip movements in childhood hip disorders

SUMMARY

After the reproducibility of measurement of hip joint motion by different techniques was ascertained, the ranges of motion of hips of 325 normal schoolchildren ages 5 to 14 years were measured with a fluid level goniometer. All movements of the hip decreased in a nonlinear fashion with increasing age. The regression line with the closest fit to the mean values of each hip movement was that obtained by applying the sixth-order equation. A grid was designed to record the ranges of movement of the hip. The ranges of movement of 93 children with pathology in one or both hips were measured by the same technique and marked on the grid. Characteristic abnormal grid patterns were noted for each condition. Careful documentation of alterations in hip joint movement in children with symptoms related to the hip can be of value in establishing the diagnosis of the underlying pathology.

Thymidylate synthase activity and the cell growth are inhibited by the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine

Employing thymidylate synthase (TS) (5, 10-CH2-H4PteGlu: dUMP C-methyltransferase, EC 2.1.1.45), a key target enzyme in chemotherapy, the biological activity of the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine (DTB) isolated from the Indian medicinal plant Alangium lamarckii has been evaluated and assessed for the first time. The TS employed in the present studies was purified from Lactobacillus leichmannii. The DTB was demonstrated to exhibit potent cytotoxicity and inhibited the cell growth of L. leichmannii, and DTB potently inhibited TS activity (IC50 = 40 microM). The DTB concentrations > 80 microM resulted in a total loss of the TS activity, thus suggesting that the beta-carboline-benzoquinolizidine alkaloid is a promising potential antitumor agent. The DTB binding to TS appears to be irreversible and tight through a possible covalent linkage. Although DTB strongly binds to DNA, it is not known whether DTB binds to RNA associated with TS. Inhibition kinetics showed that TS has a Ki value of 7 x 10(-6) M for DTB and that the inhibition is a simple linear "noncompetitive" type.

Purification and characterization of dihydrofolate reductase from Lactobacillus leichmannii

Dihydrofolate reductase (DHFR) (5,6,7,8-THF: NADDP+ oxidoreductase, EC 1.5.1.3) was purified 205-fold to apparent homogeneity from the crude extracts of Lactobacillus leichmannii. It has UV absorption maxima at 280 nm, M(r) of 20,000, Stokes radius of 0.34 nm and a S20.w value of 0.12 S. The preparation showed the presence of 168 amino acid residues with threonine and lysine as the NH2- and COOH- terminal end-groups respectively and a single reactive sulfhydryl group. pCMB inhibited the enzyme activity (IC50 = 2 microM). The enzyme has a pH optimum of 7.4 and is thermally inactivated at > 35 degrees C. It is activated by 0.1 M KCl and KI and 2 M urea. 3-4 M urea completely inactivated the enzyme. Enzyme has Km values of 3.5 microM and 6.2 microM for NADPH and DHF respectively, and a Ki value of 7 nM for MTX, the inhibition being competitive.

Inhibition of dihydrofolate reductase and cell growth activity by the phenanthroindolizidine alkaloids pergularinine and tylophorinidine: the in vitro cytotoxicity of these plant alkaloids and their potential as antimicrobial and anticancer agents

The phenanthroindolizidine plant alkaloids pergularinine (PGL) and tylophorinidine (TPD) isolated from the Indian medicinal herb Pergularia pallida have been evaluated for their biological activity and assessed for the first time employing dihydrofolate reductase (DHFR) (5,6,7,8-THF: NADP(+) oxidoreductase, EC 1.5.1.3) as the probe in the present investigations. The enzyme is a key target in cancer chemotherapy and has been purified from Lactobacillus leichmannii. Cytotoxicity studies showed that both PGL and TPD are potently toxic and inhibited the growth of L. leichmannii cells (IC(50)=45 and 40 microM, respectively). Both the alkaloids significantly inhibited DHFR activity (IC(50)=40 and 32 microM for PGL and TPD, respectively). Alkaloid concentrations greater than 75-95 microM resulted in a complete loss of DHFR activity. Our results are suggestive of the alkaloids as potential antimicrobial and antitumour compounds. Alkaloid binding to DHFR is slow and reversible. Inhibition kinetics revealed K(i) values of 9x10(-6) M and 7x10(-6) M for PGL and TPD, respectively for the enzyme and inhibition in both the cases was a simple linear 'non-competitive' type.

Inhibition of thymidylate synthase by pergularinine, tylophorinidine and deoxytubulosine

The activity of thymidylate synthase (TS) purified in our laboratory from Lactobacillus leichmannii was inhibited by pergularinine (PGL) and tylophorinidine (TPD) and deoxytubulosine (DTB) isolated from the Indian medicinal plants Pergularia pallida and Alangium lamarckii respectively. Cytotoxicity studies showed that cell growth of L. leichmannii was inhibited (IC50 = 40-45 microM) by all the three alkaloids, the concentrations > 80-90 microM resulting in complete loss of the enzyme activity. Ki values of the enzyme calculated from Lineweaver-Burk and Dixon plots for PGL, TPD and DTB were 10 x 10(-6) M, 9 x 10(-6) M and 7 x 10(-6) M respectively. These are typed as 'non-competitive' inhibitors of TS. All the three alkaloids inhibited (IC50 = 50 microM) the elevated TS activity of leukocytes in cancer patients with clinically diagnosed chronic myelocytic leukemia (n = 10), acute lymphocytic leukemia (n = 8) and metastatic solid tumours (n = 3).

Crystallization and preliminary x-ray diffraction studies of a Bowman-Birk inhibitor from Vigna unguiculata seeds

A Bowman-Birk type trypsin/chymotrypsin inhibitor isolated from Vigna unguiculata seeds has been crystallized. Crystals were grown using the vapour-diffusion method at pH 4.0 using citrate/phosphate as a buffer and 30% saturated ammonium sulfate as precipitant. The crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 32.4, b = 61.8, c = 32.9 A, beta = 114.5 degrees. The Matthews coefficient calculated assuming two molecules in the asymmetric unit was 1.95 A(3) Da(-1), which corresponds to a 37% solvent content. X-ray data were collected to 2.5 A resolution from a flash-frozen crystal. The structure was solved using the molecular-replacement method using tracy soybean inhibitor structure (PDB entry 1pi2) as a model.

Biomarkers of liver regeneration allow early prediction of hepatic recovery after acute necrosis

Acute toxic hepatic necrosis is common and may be fatal. Predicting clinical outcome may be aided by following serum markers that could indicate recovery or may signify massive (substantial) destruction of functional liver mass. Previously, in a published case of chloroform poisoning, we serially assayed serum biomarkers of hepatocellular necrosis (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, lactate dehydrogenase) and markers of hepatocellular regeneration (alpha-fetoprotein, retinol-binding protein, gamma-glutamyl transferase, and des-gamma-carboxyprothrombin). We noted a decline in necrotic markers and a synchronous elevation in regenerative markers, which could be suggestive of a favorable outcome in similar cases. We now report 6 Amanita mushroom poisonings with favorable outcome and 2 fatal acetaminophen poisonings in which the same markers were observed. Our results further support our hypothesis that a sustained decline in serum markers of hepatocyte necrosis with a concurrent elevation in regenerative markers could aid in prediction of favorable outcome in patients with acute liver injury.

Periodicity in marine phosphorus burial rate

There have been arguments both for and against a periodicity of 26-33 million years (Myr) in terrestrial and extraterrestrial records. The best way to identify such periodicity is the analysis of geomarine evolutionary records. We have analysed the marine sedimentary phosphorus burial rate (PBR), as fluctuations in this rate are strong indicators of the coupling of climate, continental weathering and ocean primary productivity. We find a statistically significant harmonic component of 33 +/- 3 Myr against the estimated robust background noise spectrum, supporting the idea that geomarine processes are cyclic.

Crystallization and preliminary X-ray studies of the basic lectin from the seeds of Artocarpus hirsuta

The basic lectin from Artocarpus hirsuta specific towards methyl alpha-galactose has been purified and crystallized using the hanging-drop vapour-diffusion method with ammonium sulfate as precipitant. Three different crystal forms, orthorhombic I, orthorhombic II and hexagonal, were grown under the same crystallization conditions. The orthorhombic forms belonged to space group P212121 with unit-cell dimensions a = 92.9, b = 99.8, c = 166. 2 A and a = 89.9, b = 121.9, c = 131.6 A, respectively. The unit-cell dimensions of the hexagonal form were a = b = 84.1 and c = 271.7 A and the space group was P6122.

Hepatic hyperplasia and cancer in rats: alterations in copper metabolism

We previously demonstrated that rats exposed to the peroxisome proliferator (PP) diethylhexylphthalate (DEHP) had reduced serum ceruloplasmin (CP) oxidase activity, which suggests tissue copper deposition. Copper is highly toxic in excess, and results in cellular damage and hepatocellular carcinomas (HCC). This study addresses changes in expression of copper-related genes and metal accumulation in hyperplastic liver and tumors induced by PP. Male rats were fed diets containing DEHP or clofibrate (CLF) for 3-60 days (hyperplasia) and 4-chloro-6-(2,3 xylidino)-2-pyrimidinyl-thio(N-beta-hydroxyethyl) acetamide for 10 months (HCC). During hyperplasia, an immediate and progressive decrease in serum CP activity was observed (P < 0.05), as were reductions in mRNA levels for both CP and Wilson's disease gene (WD gene, a P-type ATPase) (P < 0.05). Tumor-bearing rats had lower serum CP activity (P < 0.05), and CP and WD gene mRNA levels were reduced in tumors (P < 0.05), and in liver surrounding tumors (SL) (P < 0.05). Metallothionein mRNA showed no consistent changes during hyperplasia. Tumors showed a 2.5-fold induction of metallothionein mRNA (P < 0.05), and a 1.2-fold increase in SL. Temporal increases in liver copper content occurred during hyperplasia, with increases of 2-fold (DEHP) and 3.3-fold (CLF) at 60 days (P < 0.05). Copper content was 2.2-fold higher in tumors (P < 0.05) and 1.7-fold higher in SL; iron did not increase and zinc decreased temporally. Thus, copper accumulation and changes in copper-related gene expression may be contributing factors in liver neoplasia in PP-treated rats. Loss of CP results in decreased free radical scavenger capacity and thus may enhance oxidative damage induced by PPs.

Elevated blood ethanol levels caused by ‘non-alcoholic’ beer

With the availability of non-alcoholic beer, many patients are substituting non-alcoholic beer for regular beer. Moreover, several clinicians advocate the use of non-alcoholic beer by alcoholics when there is a possibility of relapse. However, patients with alcoholic end-stage liver disease can accumulate substantial circulating ethanol levels even when they consume non-alcoholic beer. We present a case of a patient with end-stage liver disease who achieved a blood alcohol level of 57 mg/dL after drinking non-alcoholic beer.

Dihydrofolate reductase and cell growth activity inhibition by the beta-carboline-benzoquinolizidine plant alkaloid deoxytubulosine from Alangium lamarckii: its potential as an antimicrobial and anticancer agent

Beta-carboline-benzoquinolizidine plant alkaloid deoxytubulosine (DTB) was evaluated and assessed for the first time for its biochemical and biological activity employing the biomarker dihydrofolate reductase (DHFR) (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) as the probe enzyme, a key target in cancer chemotherapy. DHFR, employed in the present investigations was purified from Lactobacillus leichmannii. DTB, isolated from the Indian medicinal plant Alangium lamarckii was demonstrated to exhibit potent cytotoxicity. The alkaloid potently inhibited the cell growth of L. leichmannii and the cellular enzyme activity of DHFR (IC50=40 and 30 microM for the cell growth and enzyme inhibitions, respectively). DTB concentrations >75 microM resulted in a total loss of the DHFR activity, thus suggesting that the beta-carboline-benzoquinolizidine plant alkaloid is a promising potential antitumor agent. Our results are also suggestive of its potential antimicrobial activity. DTB binding to DHFR appears to be slow and reversible. Inhibition kinetics revealed that DHFR has a Ki value of 5x10(-6) M for DTB and that the enzyme inhibition is a simple linear 'non-competitive' type.

beta-Carboline-benzoquinolizidine alkaloid deoxytubulosine inhibits thymidylate synthase activity in leukemic leukocytes from patients with chronic myeloblastic leukemia and acute lymphoblastic leukemia

Precursor 2'-deoxythymidine 5'-monophosphate for DNA biosynthesis is supplied by thymidylate synthase (TS) (EC 2.1.1.45) through a de novo pathway and the enzyme levels are elevated in malignancy. TS is therefore a key target for cancer chemotherapy. Human leukocyte TS levels in patients with chronic myeloblastic leukemia (CML) and acute lymphoblastic leukemia (ALL) are highly elevated (66- and 33-fold, respectively) compared to the low baseline activity of normal healthy controls. Preliminary screening tests for the antitumor activity of the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine (DTB) (isolated from the Indian medicinal plant Alanguim lamarckii) were performed employing in vitro inhibition studies on the leukemic leukocyte TS as the probe enzyme. Enzyme activity of the leukemic leukocytes was potently inhibited by DTB (IC50 = 50 microM) in both CML and ALL. The emetine alkaloid DTB was assessed for its biochemical and biological evaluation for the first time as a potential antileukemic agent.

Reversible inhibition by pyridoxal 5'-phosphate and irreversible inactivation by urea and guanidine hydrochloride of thymidylate synthase from Lactobacillus leichmannii

Pyridoxal 5'-phosphate reversibly inhibited thymidylate synthase from Lactobacillus leichmannii. The inhibition was competitive with dUMP (Ki = 1 microM) and non-competitive with 5,10-CH2-THF (Ki = 0.08 microM). Treatment of native or pCMB-treated enzyme with urea (5 M) or guanidine hydrochloride (4 M) resulted in inactivation and dissociation of the homodimer (74 kDa) into monomer (37 kDa).

Novel euglycemic and hypolipidemic agents. 1

A series of [[(heterocyclyl)ethoxy]benzyl]-2,4-thiazolidinediones have been synthesized by the condensation of corresponding aldehyde 1 and 2,4-thiazolidinedione followed by hydrogenation. Both unsaturated thiazolidinedione 2 and its saturated counterpart 3 have shown antihyperglycemic activity. Many of these compounds have shown superior euglycemic and hypolipidemic activity compared to troglitazone (CS 045). The indole analogue DRF-2189 (3g) was found to be a very potent insulin sensitizer, comparable to BRL-49653 in genetically obese C57BL/6J-ob/ob and 57BL/KsJ-db/db mice. Pharmacokinetic and tissue distribution studies conducted on BRL-49653 and DRF-2189 (3g) indicate that these drugs are well-distributed in target tissues. On the basis of euglycemic activity as well as enhanced selectivity against reduction of triglycerides in plasma, DRF-2189 (3g) has been selected for further evaluation.

Inhibition of thymidylate synthase and cell growth by the phenanthroindolizidine alkaloids pergularinine and tylophorinidine

Biological activity of the phenanthroindolizidine alkaloids pergularinine (PGL) and tylophorinidine (TPD) isolated from the Indian medicinal herb Pergularia pallida has been evaluated and assessed for the first time employing thymidylate synthase (TS) (5,10-CH2H4 PteGlu: dUMP-C-methyltransferase, EC 2.1.1.45), a key target enzyme in cancer chemotherapy. TS used in the present investigations was purified from Lactobacillus leichmannii. Toxicity studies showed that PGL and TPD were potently toxic and inhibited growth of L.leichmannii cells. Both PGL and TPD significantly inhibited TS activity (IC50 = 40 and 45 microM, respectively). PGL concentrations > 80 microM and TPD concentrations > 90 microM resulted in a complete loss of the TS activity, thus suggesting that both these phenanthroindolizidine alkaloids are promising potential antitumor agents. Our results show that the alkaloid-binding to TS is irreversibly tight through a probable covalent linkage. Inhibition kinetics reveal that the enzyme has Ki values of 10 x 10(-6) and 9 x 10(-6) M for PGL and TPD, respectively and that the inhibition in both the cases is a simple linear 'noncompetitive' type.

Hepatic hyperplasia and cancer in rats: metabolic alterations associated with cell growth

BACKGROUND & AIMS

We showed previously that the peroxisome proliferators di(2-ethylhexyl)phthalate (DEHP), clofibrate, and 4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyl)acetamide (BR931) alter hepatic sex steroid metabolism and receptor expression during induction of hepatic hyperplasia and hepatocellular carcinoma (HCC) in rats. The aim of this study was to identify metabolic changes associated with cell growth during hyperplasia and HCC.

METHODS

Hepatic hyperplasia was induced in male rats by a diet containing DEHP and clofibrate for 3-60 days. HCC was induced by feeding a diet containing BR931, a more potent hepatocarcinogen, for 10 months.

RESULTS

Cholesterol biosynthesis was depressed in hyperplastic livers but increased in HCC. Glucose-6-phosphate dehydrogenase (G6PD) activity was inhibited in hyperplastic liver as well as in HCC, whereas malic enzyme activity increased severalfold. Protein and messenger RNA (mRNA) levels for both G6PD and malic enzyme increased in hyperplastic livers and HCC. mRNA levels for 3-hydroxy-3-methylglutaryl-coenzyme A reductase decreased in hyperplasia and increased in HCC, whereas low-density lipoprotein receptor mRNA increased in hyperplasia and decreased in HCC.

CONCLUSIONS

Neoplastic cells acquire a growth advantage by their capacity to synthesize cholesterol and obtain reduced nicotinamide adenine dinucleotide phosphate by the malic enzyme pathway when G6PD activity is inhibited by peroxisome proliferators.

Self-enucleation in depression: a case report

Self- enucleation is a rare and an extreme form of self - mutilation, most commonly reported in schizophrenia. Many forms of self - injuries have been described in depression. However severe form of self- mutilation without suicidal intention, especially self- enucleation is rarely reported. In the present case self- enucleation is described as an expression of aggression in a depressive patient threatened with inter-personal loss. Aggression turned inwards is one of the major psychodynamic explanations in depression. In depressive syndrome self- mutilation, whether mild or severe is an expression of loss of affective (aggression) control.

Sex steroid metabolism and receptor status in hepatic hyperplasia and cancer in rats

BACKGROUND & AIMS

Both androgenic and estrogenic steroids have been implicated in the development and course of several liver diseases, including hepatocellular carcinoma. The aim of this study was to investigate temporal changes in hepatic estrogen and androgen receptors and hormone metabolism in a rat model of liver hyperplasia and carcinogenesis.

METHODS

Rats were fed hepatocarcinogenic peroxisome proliferator agents for 3 days to 10 months. Livers were examined for proliferation markers, activity and cellular distribution of sex steroid receptors, and key enzymes in sex hormone homeostasis.

RESULTS

At all times, liver weight and proliferation markers in treated rats were increased. Early exposure resulted in increased nuclear estrogen and androgen receptor activity in treated rats. Tumors that developed after 9-10 months showed a marked decrease in estrogen receptor activity and, in contrast, an increase in androgen receptor activity, as did liver surrounding the tumors. Both short-term and long-term exposure to the carcinogens resulted in dramatic reductions in steroid metabolism.

CONCLUSIONS

This study supports the thesis that, in preneoplastic stages such as hyperplasia, there is an elevation of both receptor activities and that the progression from hyperplasia to cancer results in suppression of estrogen receptor expression but maintenance of androgen receptor.

Inhibition by dehydroepiandrosterone of growth and progression of persistent liver nodules in experimental rat liver carcinogenesis

Dehydroepiandrosterone (DHEA) inhibits the development of early pre-neoplastic lesions and prevents tumor development in various tissues when given to animals during the initiation/promotion stages of carcinogenesis. Our purpose was to evaluate whether DHEA can also arrest the growth and progression of late lesions, such as persistent nodules (PNs) of rat liver. Male F344 rats were subjected to initiation by diethylnitrosamine followed by selection according to the "resistant hepatocyte" (RH) protocol. Fifteen weeks after initiation, when PNs were present in the liver, the rats were fed a diet with/without 0.6% DHEA for a maximum of 15 weeks. Glucose-6-phosphate dehydrogenase (G6PD) activity was 17- to 20-fold higher in PNs than in normal liver 15-30 weeks after initiation. It significantly decreased, in both liver and PNs, 16 hr after starting DHEA feeding. Further DHEA feeding for 3-15 weeks decreased G6PD activity by 55-58% in both tissues. Eight weeks after starting DHEA, a fall in the proportion of labeled cells, after continuous contact with 3H thymidine for 7 days, was found in nodules. Treatment for 15 weeks with DHEA caused a marked decrease in the number of nodules per liver, as well as in the incidence of PNs with diameters of 3-6 and > 6 mm, respectively, while it did not affect PNs with diameters < 3 mm. Nodules showing patterns of malignant transformation were present in 40% of rats not treated with DHEA, but not in DHEA-treated rats. All of 8 surviving rats not treated with DHEA had carcinomas at the 56th week, while only 1 out of 4 surviving rats treated with DHEA had carcinoma. These data indicate that DHEA inhibits G6PD activity in rat liver and in PNs in vivo. This is associated with growth restraint of PNs and results in inhibition of their progression to malignancy.

Inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase activity and gene expression by dehydroepiandrosterone in preneoplastic liver nodules

Previous work has demonstrated that dehydroepiandrosterone (DHEA) strongly inhibits growth and de novo cholesterol (CH) biosynthesis in preneoplastic rat liver. Administration of a mixture of 4 ribo- or deoxyribonucleosides of adenine, guanine, cytosine and uracil/thymine, prevents growth inhibition but not inhibition of CH synthesis. The purpose of this paper was to identify the site of inhibition of CH synthesis by DHEA. Persistent nodules (PNs) were induced, in diethylnitrosamine-initiated male F344 rats, by 'resistant hepatocyte' protocol. Fifteen weeks after initiation, nodule bearing rats and normal controls received a diet containing 0.6% DHEA for 3 weeks. They were then killed. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) activity and mRNA levels were 18- and 14-fold higher, respectively in nodules than in normal liver. DHEA strongly inhibited HMGR activity in both tissues in vivo, but had a slight effect on HMGR activity, when added in vitro to the reaction mixture for determination of this activity. In vivo DHEA treatment caused a 65% decrease in the level of HMGR mRNA in PNs, which, however, does not seem to completely account for the decrease in HMGR activity (83%). Low density lipoprotein receptor (LDL-R) mRNA level underwent a slight decrease in PNs, with respect to control liver, which did not lead to a significant decrease in 125I-LDL binding to LDL-R. DHEA treatment caused 30% and 24% increases in LDL-R expression and 125I-LDL binding, respectively, in nodules. These observations indicate that in addition to HMGR gene expression, increased influx of LDL into preneoplastic cells may contribute to the deregulation of mevalonate synthesis by DHEA. The observation that HMGR activity and gene expression were still 3- to 5-fold higher in PNs of DHEA-treated rats than in control liver, and previous findings of preneoplastic liver cell growth in the presence of relatively low CH synthesis, suggest that even relatively low levels of mevalonate are sufficient for the growth of preneoplastic liver cells.

Serum-ethanol determination: comparison of lactate and lactate dehydrogenase interference in three enzymatic assays

Gas chromatography is considered to be the reference method for ethyl alcohol determination. However, enzymatic ethanol assays have been developed for use in the clinical laboratory by several commercial vendors. Essentially, these assays utilize the oxidation of ethyl alcohol to acetaldehyde with concurrent reduction of nicotinamide adenine dinucleotide (NAD) to NADH while monitoring the increase in absorbance at 340 nm. The increase in absorbance is theoretically proportional to the ethanol concentration in the sample. Previously, several authors reported that increased concentrations of lactate and lactate dehydrogenase (LDH) can cause false-positive results with certain enzymatic ethyl alcohol assays. In the present investigation, we further studied the interference of lactate and LDH in three enzymatic assays. Apparent ethyl alcohol concentrations in serum spiked with lactate and LDH, as well as patient and autopsy samples, were determined by the Syva, Abbott, and Roche enzymatic assays and by gas chromatography. The effect of coenzyme depletion on the rate of reaction and the interference of hemolysis were also investigated. Based on our results we suggest that coenzyme depletion plays a major role in the severity of the false-positive ethyl alcohol result, and the interference from hemolysis has a negligible effect on these results. We also confirm the previous studies in showing that elevated serum-lactate and LDH concentrations can result in varying degrees of false-positive ethyl alcohol concentrations in the three enzymatic assays. This should be taken into consideration in the management of patients in a tertiary care medical center.

The significance of the cholesterol biosynthetic pathway in cell growth and carcinogenesis (review)

Cholesterol is widely distributed in the animal kingdom and occurs in all cell membranes. Even though the majority of body cholesterol is synthesized by the liver and secreted as circulating lipoproteins, all cells in the body have genomic information for cholesterol biosynthesis. Cholesterol biosynthesis is under feedback regulation, and the cellular and circulating cholesterol levels are tightly regulated at several points, such as the rate limiting enzyme 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase and farnesyl pyrophosphate synthetase and at the low density lipoprotein (LDL) receptor. The cholesterol content and the rate of cholesterol biosynthesis are elevated in proliferating normal tissues and tumors. Cholesterol biosynthesis happens much before DNA synthesis, and inhibiting cholesterol biosynthesis inhibits cell growth, suggesting a linkage between the cholesterol and DNA synthetic pathways. The exact nature of this linkage is not known. However, recent evidence that the farnesyl moiety in the cholesterol biosynthetic pathway is necessary for the activation of G-proteins, and of the ras oncoprotein P21 has provided a probable basis for understanding this linkage, through signal transduction pathways. Thus, farnesylation of G proteins and ras oncoprotein P21 underscores the importance of the cholesterol biosynthetic pathway in cell growth and carcinogenesis. During normal cell growth and differentiation, LDL acts as a negative growth regulator and growth factors as positive signals, the neoplastic cell achieving autocrine growth due to the activation of protooncogens. It is interesting to note that in several types of cancer, the ras gene is mutated; these mutations could increase GTP binding, and lead to an activated p21. The activation of p21 would then be aided by continuous farnesylation due to stimulation of the cholesterol biosynthetic pathway in tumors. The cholesterol biosynthetic pathway, and ras p21 could therefore be used as targets for chemoprevention of cancer.

Denaturation of pteroylpoly-gamma-glutamyl hydrolase from chicken liver by urea, thiourea and guanidine hydrochloride: altered catalytic properties of the enzyme activated by urea

The effects of varying concentrations of urea, thiourea and guanidine hydrochloride on the enzyme activity and the isoenzymic polypeptide association of pteroylpoly-gamma-glutamyl hydrolase (EC 3.4.22.12) from chicken liver were studied. Incubation of the enzyme at 4 degrees C with low concentrations of the buffered (100 mM sodium acetate containing 1% ascorbate, pH 4.1) solutions of urea (0.55 M) and guanidine hydrochloride (0.05 M) resulted in stimulation (5- and 2-fold respectively) of the activity of the enzyme whereas at higher concentrations of the denaturants (6 M urea, 1 M thiourea or 2 M guanidine hydrochloride) the enzyme was completely inactivated. However, there was no enzyme activation in response to thiorea treatment. Under specific denaturing conditions the association of two isoenzymic polypeptides was studied. The 0.55 M urea- and 0.05 M guanidine hydrochloride-activated enzyme displayed its disaggregated nonidentical polypeptides I and II (M(r) = 41,000 and 17,300 respectively) on Sephadex G-100 gel filtration, SDS-PAGE and sedimentation analyses. The 8 M urea- and 3 M guanidine hydrochloride-inactivated enzyme on the other hand exhibited a single protein aggregate species of an M(r), 57,000 like the native enzyme. Both unmodified native enzyme and the pCMB-modified PtepolyGlu hydrolase responded similarly to these denaturants. The two constituent active polypeptides polyp-I and polyp-II of the heterodimeric gamma-glutamyl glutamyl hydrolase are dissociated in the presence of 0.55 M urea as evident from the PAGE analyses. Some catalytic properties of the activated enzyme were studied and compared with those of the native enzyme. The urea-activated enzyme displayed a shift in the second pH optimum of the double pH-activity profile (optima at pH 4.1 and pH 5.2) from pH 5.2 to pH 6.0. The activated enzyme has a Km value of 0.59 x 10(-6) M (Vmax, 0.10) for 5-CH3-H4PteGlu4 while the native enzyme has the Km of 0.83 x 10(-6) M (Vmax, 0.03) for this substrate. When the reaction mixtures were incubated with the urea-activated gamma-glutamyl hydrolase, a maximum stimulatory effect on the enzyme activity was observed with the bivalent metal ion Ca2+ whereas the most potent inhibitory effect was observed with the trivalent anion citrate.

Di(2-ethylhexyl)phthalate-induced changes in liver estrogen metabolism and hyperplasia

Exposure to a common phthalate, di(2-ethylhexyl)phthalate (DEHP), is associated with liver hyperplasia prior to the development of hepatocellular carcinoma in rodents. The exact mechanism of liver hyperplasia as well as tumorigenesis by this agent is not known. Since other lines of evidence point to estrogens as mediators of liver hyperplastic changes, we investigated whether DEHP exposure might alter hepatic estrogen metabolism and induce hyperplasia. Male Fischer 344 rats were fed either control or 1.2% DEHP-containing diets and sacrificed after 4, 8 and 16 weeks of exposure; activities of several sex hormone-responsive markers were measured. Rats fed DEHP had significantly increased serum estradiol levels, but hepatic activity of both cytosolic and nuclear estrogen receptor (ER) was significantly reduced. The serum content of ceruloplasmin, an estrogen-responsive protein synthesized by the liver, was also reduced, perhaps as a consequence of loss of ER activity. The rise in serum estradiol in DEHP-treated rats may be explained by the observation that these rats showed significant losses in hepatic activity of both a major male estrogen-metabolizing enzyme, estrogen 2-hydroxylase, and a male-specific estrogen-sequestering protein. In contrast to reductions in these activities, the expression of proliferating cell nuclear antigen and mRNAs for both ER and fos increased significantly as a result of exposure to DEHP. Our results suggest that changes in estrogen metabolism, receptor activity and activation of genes for cell proliferation are among the earliest metabolic alterations induced by DEHP. These changes together with the induced hyperplasia could play a crucial role in hepatocellular carcinoma development as a result of continuous exposure to DEHP.

Psychiatric morbidity in college students and illiterate youths

The profile of psychiatric morbidity in university students in a general hospital psychiatric clinic was studied and compared with age matched illiterate youths. Students represented 5.1% of the clinic population and illiterate youths represented 3.1%. The majority of ill students were males, unmarried and from a rural area. In both groups 75% of cases sought medical help on their own, but 42% of students solicited psychiatric help directly, in contrast to 11% of illiterate youths. Students reported relatively high role specific stress factors. In contrast to results of student surveys and university health centers, we found an equal representation of psychoses and non-psychoses, a lower representation of problems of under achievement and no representation of alcohol or drug abuse.

Pteroyl- and tetrahydropteroylpolyglutamate effects on the catalytic activity of thymidylate synthase from Lactobacillus leichmannii: a novel method for determining gamma-glutamyl chain lengths of the folylpolyglutamates

Tetrahydropteroylpolyglutamates with longer gamma-glutamyl chain lengths have been found to act as better cofactors than the corresponding monoglutamates for the activity of thymidylate synthase, (5, 10-CH2H4PteGlu: dUMP C-methyltransferase, EC 2.1.1.45) purified from Lactobacillus leichmannii. Contrarily, the pteroylpolyglutamates (unreduced forms) with longer gamma-glutamyl chain lengths act as powerful inhibitors of the same enzyme, the I50 being 2 microM for the tetraglutamate, and inhibition is competitive. The Km and Ki values for the synthetic folylpolyglutamates are identical to those obtained for the natural folylpolyglutamyl forms isolated from Torula yeast (Candida utilis) by the author earlier. A rapid novel method is suggested that could be conveniently used to determine the gamma-glutamyl chain lengths of the folylpolyglutamates employing the direct or indirect linear proportionality relationship observed between the number of gamma-glutamyl residues linked and the Ki and Km values of the enzyme considering the state of oxidation/reduction of the pteridine moiety and the 1-C substituents attached.

Physico-chemical properties of thymidylate synthase from Lactobacillus leichmannii: thiol groups, amino acid composition and the terminal end-groups

Thymidylate synthase (5,10-methylenetetrahydrofolate: deoxyuridylate C-methyltransferase, EC 2.1.1.45) from Lactobacillus leichmannii was completely inactivated after 5 min of heat treatment at 55 degrees C. A remarkable synergistic effect with no loss in activity was noted when 10(-3) M dUMP was added to the enzyme before subjecting to heat treatment. The enzyme got activated in the presence of 2-mercaptoethanol (75 mM) and inhibited by pCMB (I50 = 5 microM). It had 2 free sulfhydryl groups and a single disulfide bond. The two identical subunits of the 74 kDa dimer were possibly bonded by a single disulfide linkage. It had a total of 652 amino acids with methionine as the amino-terminal and alanine as the carboxy-terminal amino acid residues. The carboxy-terminal end-group alanine was preceded by valine, lysine and proline sequentially in that order.