Torsional performance of canine femoral osteotomy union

This study allows the establishment of a protocol for standardizing the technical methodology of canine surgery for mechanical testing. Twenty mongrels were divided into 4 groups of 5 dogs each. All dogs had one femur selected as the test bone and the contralateral as paired control. The test femur was osteotomized and plated. The dogs were sacrificed at 7, 10, 13 and 16 weeks according to their group designation to determine healing of the osteotomy. Both test and control femora were tested to fracture in torsion using a computerized torsion machine. Various mechanical parameters were studied with the age of osteotomy union. The study found that all bones sustained spiral fractures through the osteotomy site. The maximum torque capacity and stiffness increased with age of union. There is an apparent biphasic pattern in the remodelling process. Up till the 13th week there was a decline in the polar moment of inertia and a rise in the torsional stress with an increase in strength. We postulate that this was due to a reduction of the outer diameter of the external bridging callus. After the 13th week, there was a reversal in the process and the outer diameter of the callus increased. The findings provide a baseline reference for future studies involving osteotomy healing as is necessary in bone allograft reconstruction and bone transport.

A single point mutation (Trp72-->Arg) in human apo(a) kringle 4-37 associated with a lysine binding defect in Lp(a)

Human lipoprotein(a) or Lp(a) binds, like plasminogen, to lysine Sepharose. However, contrary to plasminogen in which kringles 1 and 4 have been implicated, the binding site or sites on apo(a), the specific glycoprotein of Lp(a), have not been determined. For the first time we now report the occurrence of a human Lp(a) that has a mutant form of apo(a) where Arg has replaced Trp in position 72 of kringle 4-37 and is unable to bind to lysine Sepharose. This observation suggests that Trp72 of apo(a) kringle 4-37 may play a dominant role in lysine binding. Lysine binding has been associated with the thrombogenic potential of Lp(a). Thus, the Trp72-->Arg mutation may render Lp(a) 'benign' from the cardiovascular viewpoint.

Successful resection of a minute icteric hepatocellular carcinoma--case report

A 38-year-old male was admitted to our department with jaundice. Imaging studies including ultrasonography, ERCP, PTC and computed tomography (CT) revealed a hilar lesion. Right hepatic lobectomy, caudate lobectomy, excision of CBD and restoration of biloenteric continuity was performed. Pathological examination showed an icteric hepatoma (1.2 x 0.8 x 0.8 cm in size) originating in the caudate lobe. The tumor thrombus occupied the common hepatic duct and the right intrahepatic duct. The postoperative course was fairly unremarkable, and the patient has remained in good health for four years after surgery without any sign of recurrence.

Characterization of cAMP-dependent inhibition of LPS-induced TNF alpha production by rolipram, a specific phosphodiesterase IV (PDE IV) inhibitor

Bacterial endotoxins (lipopolysaccharide or LPS) provoke shock and tissue injury by eliciting the release of toxic factors from reticuloendothelial cells. One of the principal endogenous factors involved in this process is tumor necrosis factor alpha (TNF alpha). In this study, inhibitors selective for different classes of phosphodiesterases (PDE), were examined for their effects on LPS-induced TNF alpha production by human monocytes. The selective cAMP-PDE IV inhibitors, rolipram and RO-20-1724 were capable of inhibiting LPS-induced TNF alpha production by human monocytes in a concentration-dependent manner. Rolipram was used to examine further the cellular pharmacology of PDE IV inhibitors on cytokine production. The IC50 for inhibition of LPS-induced TNF alpha production by rolipram was 0.1 microM, whereas production of IL-1 beta or IL-6 was unaffected. Furthermore, rolipram was equally effective in inhibiting TNF alpha production by a number of other stimuli. Inhibition of TNF alpha production by rolipram was associated with an elevation of intracellular cAMP, consistent with a mechanism involving phosphodiesterase inhibition. Rolipram was efficacious in suppressing LPS-induced TNF alpha mRNA expression, and at the protein level was also active when added to cultures post-stimulated with LPS. This indicates that rolipram may act at both the transcriptional and translational levels. Rolipram inhibited TNF alpha production in vivo in a rat endotoxemia model. Collectively, these data suggest that the prototypic inhibitor of PDE IV isozyme, rolipram, can effectively and selectively inhibit LPS-induced TNF alpha production through elevation of intracellular cAMP.

Pyridinyl imidazoles inhibit the inflammatory phase of delayed type hypersensitivity reactions without affecting T-dependent immune responses

The effects of pyridinyl imidazoles, specifically SK&F 105809 and its metabolite, on normal T-cell and B-cell mediated immune responses were examined and compared to the fungal macrolide immunosuppressives, cyclosporin A, FK506 and rapamycin and to the corticosteroid, dexamethasone. The orally active prodrug SK&F 105809 [2-(4-methylsulfinylphenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo [1,2-a] imidazole[ and its metabolite, SK&F 105561 [2-(4-methylthiophenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo[1,2 -a] imidazole] are dual 5-lipoxygenase (5-LO) and cycloxygenase (CO) inhibitors with potent anti-inflammatory and cytokine (IL-1/TNF) suppressive activities. The anti-inflammatory activity of SK&F 105809 and its metabolite were evaluated in an antigen-specific murine model of delayed type hypersensitivity (DTH) response, where they were found to affect only the inflammatory and not the induction phase of this response. In contrast, these compounds and other pyridinyl imidazoles (SK&F 86002 and its analog, SK&F 104351) exhibited no immunosuppressive activity under conditions where the macrolide rapamycin and the corticosteroid dexamethasone abrogated both the cellular and humoral immune responses. Thus, the ability of pyridinyl imidazoles to attenuate independently the inflammatory components of the disease without causing generalized immunosuppression enhances their profile as candidates for therapy of chronic inflammatory diseases, specifically those mediated by cytokines (e.g. IL-1, TNF) and eicosanoids.

Epstein-Barr virus-associated gastric lymphoma in Hong Kong Chinese

We report 11 cases of gastric lymphoma that harbor the Epstein-Barr virus (EBV) encoded small messenger RNA, EBER-1, detected by in situ hybridization. The cases represented 18% of 61 consecutive gastric lymphomas from three institutions in Hong Kong between 1988 and 1993. The mean age of patients was 62 years (range, 33 to 87). The male to female ratio was 5:6. Nine of the 11 (81.8%) EBER-1+ gastric lymphomas were diffuse large cell lymphomas of B-cell type without low grade components. Macroscopically these lymphomas appeared either as large noncleaved cell (centroblastic) or immunoblastic type. From the available follow-up data, five of the nine patients with B-cell lymphoma were alive and well 48, 40, 14, 13, and 12 months, respectively, after gastrectomy and chemotherapy. One patient died of postoperative pneumonia and one died of a second malignancy (esophageal squamous carcinoma) 40 months after gastrectomy. None of the EBER-1+ B-cell gastric lymphomas showed histological features characteristic of low grade lymphoma of the mucosa-associated lymphoid tissue (MALT) type reported to be common in some Western countries. Of the two patients with T-cell lymphoma, one had a pleomorphic T-cell lymphoma and the other had an angiocentric lymphoma. The former was lost to follow-up after the biopsy and the latter presented with gastric perforation and died 1.5 months after gastrectomy. It is concluded that a significant proportion of gastric lymphomas in Hong Kong Chinese are EBV-related and that they show histological features more akin to conventional node-based lymphomas than to MALT-type lymphomas.

Missense mutations in the adhalin gene linked to autosomal recessive muscular dystrophy

Adhalin, the 50 kDa dystrophin-associated glycoprotein, is deficient in skeletal muscle of patients having severe childhood autosomal recessive muscular dystrophy (SCARMD). In several North African families, SCARMD has been linked to chromosome 13q, but SCARMD has been excluded from linkage to this locus in other families. We have now cloned human adhalin cDNA and mapped the adhalin gene to chromosome 17q12-q21.33, excluding it from involvement in 13q-linked SCARMD. However, one allelic variant of a polymorphic microsatellite located within intron 6 of the adhalin gene cosegregated perfectly with the disease phenotype in a large family. Furthermore, missense mutations were identified within the adhalin gene that might cause SCARMD in this family. Thus, the adhalin gene is involved in at least one form of autosomal recessive muscular dystrophy.

Evaluation of three culture media and their combinations for the isolation of Mycobacterium tuberculosis from pleural aspirates of patients with tuberculous pleurisy

The abilities of three culture systems to detect Mycobacterium tuberculosis from 480 pleural aspirate specimens in 347 patients were compared. The systems were the Bactec 12B radiometric detection system (Bactec 12B), the Middlebrook 7H9 broth (7H9), and two solid media including one pyruvate enriched Lowenstein-Jensen slope (LJP) and one non-selective Middlebrook 7H11 agar slope (7H11). In the 116 specimens obtained from 85 patients of confirmed pleural tuberculosis for the isolation of Mycobacterium tuberculosis, the diagnostic yields were 33 (39%) cases from Bactec 12B, 24 (28%) cases from 7H9 and 21 (25%) cases from LJP/7H11, with median detection times of 18, 47.5 and 44 days respectively. Thirteen isolates were recovered by the Bactec 12B only, 9 by the 7H9 broth only, and 2 by the LJP/7H11 agar only. The use of a combination of the three culture systems substantially increased the diagnostic yield to 47% over the individual systems. These results show that a significantly greater and faster diagnostic yield can be obtained by including Bactec 12B in pleural aspirate cultures for the recovery of Mycobacterium tuberculosis.

Congenital bilateral perisylvian syndrome: analysis of the first four reported Korean patients

The advent of MRI technique has enabled the diagnosis of neuronal migration disorders(NMD) and made it possible to make "in vivo" diagnosis. Congenital bilateral perisylvian syndrome(CBPS) is a recently described disease identify characterized by pseudobulbar palsy, epilepsy, mental retardation, and migration disorders in the bilateral perisylvian area. We have identified four CBPS patients based on neuroimaging and dysarthria patterns among the candidates for epilepsy surgery. All the patients had orofacial diplegia and variable degrees of mental retardation. In the spectrographic analysis of dysarthria, the loss of specific characteristics of formants of vowels and increment of noise in the high frequency formants were observed. Epilepsy was present in all, but only one patient showed intractable seizure requiring surgical intervention. MRI was most helpful in identifying NMD and polymicrogyria in both centroparietal areas in this context. Great alertness is needed to identify this disorder to determine the etiology of epilepsy and dysarthria of uncertain origin.

A region of homozygous deletion on chromosome 9p21-22 in primary nasopharyngeal carcinoma

Using 21 microsatellite polymorphic markers spanning both p and q arms, we have performed detailed deletion mapping on chromosome 9 in 18 primary nasopharyngeal carcinomas. All 18 tumors were informative at multiple loci. Eleven of the 18 cases (61%) demonstrated allelic deletion of chromosome 9. Among these 11, 6 cases are likely to be tumors with monosomy of chromosome 9. The other 5 cases demonstrated partial deletion by showing multiple areas of allelic loss. In one of the 5 cases, a homozygous deletion region was identified which includes D9S126, D9S171, and IFNA loci at 9p21-22, situated between loci D9S161 (9p21) and D9S162 (9p21-22). The presence of a homozygous deletion strongly suggests the presence of tumor suppressor gene(s) involved in the tumorigenesis of nasopharyngeal carcinoma. The same region has been reported to include some potential tumor suppressor gene loci in other cancers. This is the first reported finding of frequent genetic loss observed on chromosome 9 in nasopharyngeal carcinomas in addition to allelic loss on chromosome 3p at specific regions. Our results suggest that tumorigenesis and progression of nasopharyngeal carcinomas, like other solid tumors, involves multiple genetic changes associated with the inactivation of tumor suppressor genes.

Independent impact of thrombolytic therapy and vessel patency on left ventricular dilation after myocardial infarction. Serial echocardiographic follow-up

BACKGROUND

It has been shown that successful reperfusion of the infarct-related artery by thrombolysis can prevent left ventricular dilation after acute myocardial infarction; these beneficial effects were detected from several days to several months after infarction. To date, however, no study has shown that these effects can be demonstrated within hours after the onset of infarction. Furthermore, data are scarce on the independent impact of thrombolytic therapy and late vessel patency on ventricular volume and function. The aim of this study was to assess separate effects of thrombolysis and patency of the infarct-related artery on left ventricular size and function by serial two-dimensional echocardiographic examinations.

METHODS AND RESULTS

We evaluated 131 consecutive patients with first acute myocardial infarction by two-dimensional echocardiography in the following sequence: days 1, 2, 3, 7, and after 3 and 6 weeks. Intravenous streptokinase was administered in 81 patients, and 50 patients were treated without thrombolysis. Left ventricular end-diastolic volume, end-systolic volume, and ejection fraction were determined from apical two- and four-chamber views using the Simpson biplane formula and normalized to body surface area. Coronary angiography was performed in 107 patients after a mean of 26.0 +/- 20.2 (mean +/- SD) days after infarction. Patency of the infarct-related artery was assessed using TIMI criteria, with 54 considered patent (TIMI 3) and 53 with TIMI grade < 3. On day 1, end-systolic volume was significantly higher in patients not receiving thrombolysis (37.7 +/- 15.3 versus 33.0 +/- 10.6 mL/m2, P = .045). End-systolic volume (ESVi) was significantly higher in patients treated without thrombolysis throughout the study, whereas significant differences in end-diastolic volume (EDVi) were detected from day 3 (P = .041) onward and in ejection fraction (EF) from day 2 (P = .025) onward, all differences becoming progressively more significant with time (6-week values: EDVi, 78.8 +/- 25.4 versus 65.9 +/- 15.7 mL/m2, P = .001; ESVi, 45.4 +/- 22.6 versus 33.9 +/- 15.1 mL/m2, P = .002; EF, 45.1 +/- 11.6% versus 50.2 +/- 10.1%, P = .018). Patients with an occluded infarct-related artery (TIMI < 3) demonstrated highly significant differences at 6 weeks compared with patients with patent vessels (EDVi, 76.8 +/- 24.7 versus 65.2 +/- 15.6 mL/m2, P = .006; ESVi, 44.6 +/- 23.3 versus 31.9 +/- 12.2 mL/m2, P = .001; EF, 45.0 +/- 11.6% versus 52.1 +/- 9.0%, P < .001), but these differences developed more slowly than that seen among the thrombolytic subgroups. Indeed, multivariate analysis demonstrated that thrombolysis was the major determinant of initial volumes (P = .08, .02, and .08 for EDVi, ESVi, and EF, respectively), while vessel patency was the overwhelming determinant of subsequent changes (P = .0033, .0002, and .0024 for EDVi, ESVi, and EF, respectively). Additionally, ventricular volumes were significantly higher and ejection fractions lower in patients with anterior versus inferior infarction, but even adjusting for these differences as well as those associated with age, sex, and initial ventricular volume, the additive and independent impact of thrombolysis and infarct vessel patency persisted.

CONCLUSIONS

These data indicate that the beneficial effect of thrombolysis on left ventricular size and function can be demonstrated in the earliest phases of acute myocardial infarction and that subsequent changes are mediated primarily through patency of the infarct-related artery. Thrombolytic therapy and late vessel patency thus have an additive and complementary impact in reducing ventricular dilation after myocardial infarction.

Genetic analysis of type 5 capsular polysaccharide expression by Staphylococcus aureus

Capsules are produced by over 90% of Staphylococcus aureus strains, and approximately 25% of clinical isolates express type 5 capsular polysaccharide (CP5). We mutagenized the type 5 strain Reynolds with Tn918 to target genes involved in CP5 expression. From a capsule-deficient mutant, we cloned into a cosmid vector an approximately 26-kb EcoRI fragment containing the transposon insertion. In the absence of tetracycline selection, Tn918 was spontaneously excised, thereby resulting in a plasmid containing 9.4 kb of S. aureus DNA flanking the Tn918 insertion site. The 9.4-kb DNA fragment was used to screen a cosmid library prepared from the wild-type strain. Positive colonies were identified by colony hybridization, and a restriction map of one clone (pJCL19 with an approximately 34-kb insert) carrying the putative capsule gene region was constructed. Fragments of pJCL19 were used to probe genomic DNA digests from S. aureus strains of different capsular serotypes. Fragments on the ends of the cloned DNA hybridized to fragments of similar sizes in most of the strains examined. Blots hybridized to two fragments flanking the central region of the cloned DNA showed restriction fragment length polymorphism. A centrally located DNA fragment hybridized only to DNA from capsular types 2, 4, and 5. DNA from pJCL19 was subcloned to a shuttle vector for complementation studies. A 6.2-kb EcoRI-ClaI fragment complemented CP5 expression in a capsule-negative mutant derived by mutagenesis with ethyl methanesulfonate. These experiments provide the necessary groundwork for identifying genes involved in CP5 expression by S. aureus.

A requirement of hydrophobic and basic amino acid residues for substrate recognition by Ca2+/calmodulin-dependent protein kinase Ia

The substrate recognition determinants of Ca2+/calmodulin-dependent protein kinase Ia were investigated by using peptide analogues based on the amino acid sequence around Ser-9 of synapsin I. The Km and Vmax for the synthetic peptide Leu-Arg-Arg-Arg-Leu-Ser-Asp-Ala-Asn-Phe are 3.9 microM and 18.5 mumol/(min.mg), respectively. Deletion of Leu at the -5 position lowers the Vmax/Km by 470-fold. The requirement for a hydrophobic residue at -5 was confirmed by the 90- to 2400-fold reduction in Vmax/Km produced by Arg, Ala, or Asp substitutions, but only 2.6-fold decrease after Phe substitution at this position. A hydrophobic residue is similarly required at the +4 position. Deletion of Phe at this position produces a 67-fold reduction, and substitution of Ala for Phe a 43-fold reduction in Vmax/Km. In contrast, substitution with Leu increases Vmax/Km by 1.8-fold. Arg at -3 is also required for recognition as shown by an approximately 240-fold decrease in Vmax/Km after Ala substitution at this position. Positions -2, -4, and +1 appear to play secondary roles in substrate recognition. Arg at -2 and -4 are positive determinants, since Ala substitution at these positions decreases Vmax/Km by 4.7- and 11-fold, respectively. Asp at +1 is a negative influence, since Ala and Leu substitutions at this position increase Vmax/Km by 2.3- and 6.3-fold, respectively. Substitution of Ala for Leu at -1 or Thr for Ser at the 0 position has little effect on phosphorylation kinetics. Thus, Ca2+/calmodulin-dependent protein kinase Ia has the minimal substrate recognition motif of Hyd-Xaa-Arg-Xaa-Xaa-(Ser*/Thr*)-Xaa-Xaa-Xaa-Hyd, where Hyd represents a hydrophobic amino acid residue.

Random amplified polymorphic DNA polymerase chain reaction (RAPD PCR) fingerprints in forensic species identification

The random amplified polymorphic DNA (RAPD) method was used to identify the species of forensic biological samples. Neither genomic DNA sequence nor two polymerase chain reaction (PCR) cycle programs is required. Only single 10-nt primer and one PCR program are used. We demonstrated that this method can be used to identify animals including bovine, goat, pig, dog, rat, rabbit, chicken, duck, and human by comparing their RAPD PCR fingerprints. This study provides a simple, fast and sensitive fingerprinting method in species identification for crime scene evidence or food products of endangered species.

Hyperammonemic encephalopathy due to essential amino acid hyperalimentation

Hyperammonemic encephalopathy has occasionally been reported in uremic patients receiving hyperalimentation with essential amino acid (EAA) as a source of nitrogen as one of the remaining treatment options when the enteric routes were prohibited. We encountered this complication in a patient with normal renal function. A rat animal model was designed to elucidate the mechanism of hyperammonemia resulting from hyperalimentation with EAA as a source of nitrogen. Sixty-four male Long-Evan rats were divided into eight groups receiving feeds ad libitum or different formula of hyperalimentation. Hyperammonemia was found in every rat given hyperalimentation with EAA as the only nitrogen source. Using the Tukey honestly significant difference test, the results were significantly higher (p < 0.001) than that of the control group which were given feeds ad libitum and those groups given hyperalimentation for the same number of days but with mixed amino acid (MAA) as the nitrogen source. Adding arginine to EAA for a further four days after initial administration of EAA hyperalimentation for three days only slightly lowered the mean serum ammonia level. When compared to that of the three-day EAA hyperalimentation group, the difference was not statistically significant. Adding arginine, citrulline, and ornithine to EAA for a further four days significantly lowered the mean serum ammonia level. When we changed EAA hyperalimentation to MAA hyperalimentation for a further four days, the mean serum ammonia level decreased dramatically to nearly normal. Hyperalimentation using EAA as the exclusive source of nitrogen resulted in hyperammonemia. A deficiency of arginine or other amino acids of the urea cycle failed to account completely for the hyperammonemia observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of the tumour suppressor gene p53 in nasopharyngeal carcinoma in Hong Kong Chinese

This study has investigated the expression of the p53 tumour suppressor gene in 41 cases of primary nasopharyngeal carcinomas (NPC) using the p53 monoclonal antibody BP53-12. Moderate p53 expression was found in 54% and strong expression in 12% of the specimens. There was no correlation between p53 expression and any of the clinicopathological parameters or survival. Surprisingly, three research groups have investigated p53 mutations in NPC and found no fresh tumour specimens to contain p53 mutations in exons 4-8 of the gene. It may be argued that as p53 overexpression has been demonstrated in 70% of the patients investigated in this study, that the mutations lie outside the 4-9 exon region. We are in the process of testing this hypothesis.

Radiolabeled polymerase chain reaction assay for detection of ras oncogene point mutations in tumors

The human ras gene plays a fundamental role in the transduction of extracellular signals to the nucleus, thereby regulating cell growth and differentiation. Point mutations in the ras gene convert it into a transforming oncogene that has been found in many solid and hematologic malignancies. We describe a rapid and sensitive assay based on a radiolabeled polymerase chain reaction followed by restriction enzyme digestion that we have adapted for differentiating between the wild-type and mutant ras genes. This assay should prove useful in the analysis of ras gene point mutations in clinical tumor specimens in which ras oncogene activation is an early event in carcinogenesis.

Radiolabeled polymerase chain reaction assay for detection of ras oncogene point mutations in tumors

The human ras gene plays a fundamental role in the transduction of extracellular signals to the nucleus, thereby regulating cell growth and differentiation. Point mutations in the ras gene convert it into a transforming oncogene that has been found in many solid and hematologic malignancies. We describe a rapid and sensitive assay based on a radiolabeled polymerase chain reaction followed by restriction enzyme digestion that we have adapted for differentiating between the wild-type and mutant ras genes. This assay should prove useful in the analysis of ras gene point mutations in clinical tumor specimens in which ras oncogene activation is an early event in carcinogenesis.

Electrostatic forces contribute to interactions between trp repressor dimers

The trp repressor of Escherichia coli (TR), although generally considered to be dimeric, has been shown by fluorescence anisotropy of extrinsically labeled protein to undergo oligomerization in solution at protein concentrations in the micromolar range (Fernando, T., and C. A. Royer 1992. Biochemistry. 31:3429-3441). Providing evidence that oligomerization is an intrinsic property of TR, the present studies using chemical cross-linking, analytical ultracentrifugation, and molecular sieve chromatography demonstrate that unmodified TR dimers form higher order aggregates. Tetramers and higher order species were observed in chemical cross-linking experiments at concentrations between 1 and 40 microM. Results from analytical ultracentrifugation and gel filtration chromatography were consistent with average molecular weight values between tetramer and dimer, although no plateaus in the association were evident over the concentration ranges studied, indicating that higher order species are populated. Analytical ultracentrifugation data in presence of corepressor imply that corepressor binding destabilizes the higher order aggregates, an observation that is consistent with the earlier fluorescence work. Through the investigation of the salt and pH dependence of oligomerization, the present studies have revealed an electrostatic component to the interactions between TR dimers.

Altered mechanical responses of malignant hyperthermic skeletal muscle during repetitive stimulation

This investigation examined the mechanical responses of malignant hyperthermic (MH) and normal porcine skeletal muscle to repetitive stimulation. Twitch and maximal tetanic tensions were not significantly different between muscle types. Tensions produced during stimulation at 20-80 Hz were significantly less in MH muscle than in normal muscle. In addition, MH muscle showed significantly greater force decline (tetanic fade) at the end of contractions evoked by 20-80 Hz stimulation. When stimulated to fatigue, both normal and MH muscle exhibited similar rates of tension decline during the initial minutes. Further stimulation caused additional decline in normal muscle, but a tension plateau in MH muscle. In all cases, normal muscle had greater magnitudes of fatigue than did MH muscle. Results show that there are marked differences between MH and normal muscle in the mechanical responses to repetitive stimulation. Due to its inability to properly regulate intracellular Ca2+ exchange, it is possible that MH muscle might be a useful tool for identifying the mechanisms of muscle fatigue in normal muscle.

Construction of a dimeric repressor: dissection of subunit interfaces in Lac repressor

Formation of the lactose repressor tetramer is postulated to involve two subunit interfaces, one primarily contributing to monomer-monomer assembly to dimer and the second to dimer-dimer association to tetramer. The latter interface requires a heptad repeat of three leucines at the C-terminus of lac repressor that is presumed to form an abbreviated coiled-coil motif [Chakerian, A. E., Tesmer, V. M., Manly, S. P., Brackett, J. K., Lynch, M. J., Hoh, J. T., & Matthews, K. S. (1991) J. Biol. Chem. 266, 1371-1374; Alberti, S., Oehler, S., von Wilcken-Bergmann, B., Krämer, H., & Müller-Hill, B. (1991) New Biol. 3, 57-62; Chen, J., & Matthews, K. S. (1992) J. Biol. Chem. 267, 13843-13850]. To strengthen the dimer-dimer interface, this motif was extended by the addition of one and two leucine heptad repeat units to the C-terminus by site-specific insertion mutagenesis. The tetrameric products displayed operator and inducer affinity essentially indistinguishable from the wild-type repressor. In order to probe the effect of the elongated coiled-coil on assembly of the repressor tetramer, the other of the two postulated subunit interfaces was disrupted by introducing a point mutation (Y282D) that yields a monomeric protein in the wild-type background. Both elongated mutant repressors were able to assemble into dimeric species, apparently due to the strengthened subunit association at the C-terminal region compared to the wild-type repressor. These results further confirm the role of a coiled-coil structure in the formation of tetramer in the lac repressor.(ABSTRACT TRUNCATED AT 250 WORDS)

A protein activator of Ca(2+)-calmodulin-dependent protein kinase Ia

A protein activator of Ca(2+)-calmodulin-dependent protein kinase Ia (CaM kinase Ia) was purified to near homogeneity from pig brain. In the final step of purification, sucrose density gradient centrifugation, CaM kinase Ia activating activity correlated with the presence of a approximately 52-kDa protein band detected by SDS-polyacrylamide gel electrophoresis. Comparison of this value with estimations of its molecular mass under nondenaturing conditions indicated that CaM kinase Ia activator is a slightly asymmetric monomer. After removal of endogenous CaM kinase Ia activator, the activity of CaM kinase Ia was 2% of its activity in the presence of a maximally stimulating concentration (15 nM) of the purified activator. In its activated state, CaM kinase Ia retained complete dependence of its activity upon Ca(2+)-CaM. The activation of CaM kinase Ia was rapid (t1/2 < 1 min) and required the combined presence of CaM kinase Ia activator, Ca(2+)-CaM, and MgATP. Similarly, in addition to MgATP, the phosphorylation of CaM kinase Ia required CaM kinase Ia activator and Ca(2+)-CaM. CaM kinase Ia activator was capable of Ca(2+)-dependent binding to CaM-Sepharose. The requirement of the combined presence of CaM kinase Ia activator, Ca(2+)-CaM, and MgATP for both the activation and phosphorylation of CaM kinase Ia is discussed in terms of potential mechanisms for CaM kinase Ia activation.