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Biomedical subjects

J J Ma

Publications and source records attributed to J J Ma.

31 records · Page 2Linked to original sources
PubMed1993

Sodium valproate: quantitative EEG and serum levels in volunteers and epileptics.

Twelve healthy adults and 12 epileptics had quantitative EEG tests while taking valproic acid. The results indicated that the total power of dominant frequency band and the frequency of dominant occipital rhythm were relatively stable in healthy awake adults. A single 400 mg oral dose of sodium valproate had similar influence on the total power of dominant frequency band in both healthy adults and epileptics. The total power of dominant frequency band tended to rise at 2 and 6 hours after medication in subjects with serum VPA concentrations reaching a peak after 2 hours. There was a tendency to rise at 4 and 8 hours in subjects with serum VPA concentrations which peaked after 4 hours. The curve of the total power with time had two peaks. A single oral dose of sodium valproate did not have a marked influence on the frequency of dominant rhythm in the occipital areas in healthy adults or in epileptics.

Adult↗
PubMed1991

The mechanical hypothesis of excitation-contraction (EC) coupling in skeletal muscle.

The mechanism of transmission in skeletal muscle EC coupling is still an open question. There is some indirect evidence in favour of the mechanical coupling hypothesis, deriving mostly from consideration of the structure of the Ca2+ release channel protein. A new functional approach is proposed, that consists in comparing the properties of the complete system--EC coupling in a skeletal muscle fibre--with those of the EC coupling molecules in bilayers. In this approach, those properties of the whole system that are not traceable to its constitutive molecules, are ascribed to the physiological interaction, and are expected to yield new information on the nature of this interaction.

Animals↗
PubMed1991

Saccharomyces cerevisiae nucleoside-diphosphate kinase: purification, characterization, and substrate specificity.

Nucleoside-diphosphate kinase is an enzyme which catalyzes the phosphorylation of nucleoside diphosphates into the corresponding triphosphates for nucleic acid biosynthesis. In this communication, we describe the purification and characterization of nucleoside-diphosphate kinase from yeast. The purified protein appears to be homogeneous by sodium dodecyl sulfate-polyacrylamide gel analysis, with a molecular weight of about 17,000-18,000. An estimate from the fast protein liquid chromatography Superose 12 gel filtration shows a native molecular weight of about 68,000 to 70,000. The results suggest that yeast nucleoside-diphosphate kinase is composed of four subunits. Substrate specificity studies show that the relative activity of nucleoside diphosphates (NDP) as phosphate acceptors is in the order of dTDP greater than CDP greater than UDP greater than dUDP greater than GDP greater than or equal to dGDP greater than dCDP greater than dADP greater than ADP; and the relative activity of triphosphate donors is in the order of UTP greater than dTTP greater than CTP greater than dCTP greater than dATP greater than ATP greater than or equal to dGTP greater than GTP. The Km and Vm of dTDP, dGDP, dCDP, dUDP, CDP, and UDP have been determined. The rate constant studies indicate that the purified NDP kinase prefers using, to a slight extent, dTDP (approximately 800 min-1) as the substrate rather than other tested deoxyribo- and ribonucleotides (350-450 min-1). The broad substrate specificity and kinetic data suggest that the enzyme is involved in both DNA and RNA metabolism.

Molecular Weight↗
PubMed1991

Cloning and sequence of the gene for heat shock protein 60 from Chlamydia trachomatis and immunological reactivity of the protein.

We isolated and sequenced the gene for the chlamydial heat shock protein 60 (HSP-60) from a Chlamydia trachomatis genomic library by molecular genetic methods. The DNA sequence derived revealed an operon-like gene structure with two open reading frames encoding an 11,122- and a 57,956-Da protein. The translated amino acid sequence of the larger open reading frame showed a high degree of homology with known sequences for HSP-60 from several bacterial species as well as with plant and human sequences. By using the determined nucleotide sequence, fragments of the gene were cloned into the plasmid vector pGEX for expression as fusion proteins consisting of glutathione S-transferase and peptide portions of the chlamydial HSP-60. HSP-60 antigenic identity was confirmed by an immunoblot with anti-HSP-60 rabbit serum. Sera from patients that exhibited both high antichlamydial titers and reactivity to chlamydial HSP-60 showed reactivity on immunoblots to two fusion proteins that represented portions of the carboxyl-terminal half of the molecule, whereas fusion proteins defining the amino-terminal half were nonreactive. No reactivity with the fusion proteins was seen with sera from patients that had been previously screened as nonreactive to native chlamydial HSP-60 but which had high antichlamydial titers. Sera from noninfected control subjects also exhibited no reactivity. Definition of recognized HSP-60 epitopes may provide a predictive screen for those patients with C. trachomatis infections who may develop damaging sequelae, as well as providing tools for the study of immunopathogenic mechanisms of Chlamydia-induced disease.

Amino Acid Sequence↗
PubMed1990

Purification and characterization of Saccharomyces cerevisiae uridine monophosphate kinase.

The SOC8 gene was isolated as an extragenic suppressor of cdc8 mutant cells. It has been suggested that SOC8 is allelic with the URA6 gene which was originally identified as a uridine monophosphate kinase. In this article, we describe the purification of the uridine monophosphate kinase from a yeast Saccharomyces cerevisae strain that overproduces the activity 8-fold. The protein was purified through Fast-Flow Q-Separose, phosphocellulose, blue-agarose, and fast protein liquid chromatography Superose 12 columns, and appears homogeneous by sodium dodecyl sulfate-polyacrylamide gel analysis. The uridine monophosphate kinase contains a single polypeptide with a molecular weight of 25,000, as evidence by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration analysis. The amino acid composition has also been determined. Substrate specificity studies show that the relative activity of nucleoside monophosphates is in order of UMP greater than dUMP, and to a lesser extent, dTMP, GMP, and dGMP. The Km and Vm of UMP, dUMP, and dTMP have been determined.

Amino Acids↗
PubMed1990

Abnormal ryanodine receptor channels in malignant hyperthermia.

Previous studies have demonstrated a defect associated with the calcium release mechanism of sarcoplasmic reticulum (SR) from individuals susceptible to malignant hyperthermia (MH). To examine whether SR calcium release channels were indeed altered in MH, SR vesicles were purified from normal and MH susceptible (MHS) porcine muscle. The Ca2+ dependence of calcium efflux rates from 45Ca2(+)-filled SR vesicles was then compared with the Ca2+ dependence of single-channel recordings of SR vesicles incorporated into planar lipid bilayers. The rate constants of 45Ca2+ efflux from MHS SR were two to threefold larger than from normal SR over a wide range of myoplasmic Ca2+. Normal and MHS single channels were progressively activated in a similar fashion by cis Ca2+ from pCa 7 to 4. However, below pCa 4, normal channels were inactivated by cis Ca2+, whereas MHS channels remained open for significantly longer times. The altered Ca2+ dependence of channel inactivation in MHS SR was also evident when Ca2+ was increased on the trans side while cis Ca2+ was held constant. We propose that a defect in a low-affinity Ca2+ binding site is responsible for the altered gating of MHS SR channels. Such a defect could logically result from a mutation in the gene encoding the calcium release channel, providing a testable hypothesis for the molecular basis of this inherited disorder.

Animals↗
PubMed1987

Calcium channel activity in a purified dihydropyridine-receptor preparation of skeletal muscle.

A purified dihydropyridine-receptor complex (DHPR) of skeletal muscle consisting of a major polypeptide of Mr 150K under reducing conditions induces divalent cation selective channels when incorporated into planar lipid bilayers. Channels were inserted into preformed planar bilayers by two techniques: (i) direct dilution of detergent-solubilized DHPR into the aqueous chambers adjacent to the bilayer membrane or (ii) reconstitution of DHPR into phospholipid vesicles followed by fusion of the preformed vesicles to the planar bilayer membrane. Unlike native membrane preparations of t-tubules, which only have one major Ca channel type of slope conductance of 12 pS in symmetrical 100 mM Ba, the purified DHPR complex induced at least two channel types with conductances of 12-14 and 22 pS. Some recordings suggest that these two channels are statistically coupled in time, i.e., that they may correspond to substrates of the same DHPR channel. Activity was found to occur spontaneously in the absence of the Ca channel agonist Bay k 8644. The 12-14-pS channel from DHPR exhibits voltage-dependent kinetics, is highly selective for barium ions, and was inhibited by micromolar nitrendipine. The 12-14-pS DHPR channel appears to be identical with functional Ca channels previously described in native t-tubules.

Animals↗
PubMed1987

Identification of conserved regions for species and subspecies specific epitopes on the major outer membrane protein of Chlamydia trachomatis.

Proteolytic peptides containing the serological epitopes present on the major outer membrane protein of Chlamydia trachomatis were studied by immunoblots. Monoclonal antibodies which have been defined by micro-immunofluorescence typing as serovar-, subspecies and species-specific were utilized. The reactivity of either serovar-specific or species-specific monoclonal antibodies in the immunoblots was similar to that in the micro-immunofluorescence test. However, monoclonal antibodies which demonstrated subspecies-specific reactivity by the micro-immunofluorescence test expressed species-specific reactivity by the immunoblot method. The serovar-specific epitope which was identified on the major outer membrane protein was lost after proteolytic digestion with Staphylococcus aureus V8 protease. Immunoblots of the proteolytic fragments identified the species-specific epitope on several peptides and the subspecies-specific epitope on fewer peptides than those in which the species-specific epitope was identified. In addition, both the species and subspecies epitopes were present on the same fragments of different serovars. The data indicate that the species epitope is on conserved regions of the major outer membrane protein and is structurally clustered with a subspecies-specific epitope.

Animals↗
PubMedDate not supplied

Total splenic infarct due to Aspergillus and AIDS.

Invasive aspergillosis is a rare but important cause of morbidity and mortality in patients with AIDS. In the majority of patients, invasive aspergillosis involves the lungs. Extrapulmonary involvement with total splenic infarction has not been previously described. We illustrate a patient who developed total splenic infarction and septic emboli to the brain from Aspergillus.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Total splenic infarct due to Aspergillus and AIDS.

Invasive aspergillosis is a rare but important cause of morbidity and mortality in patients with AIDS. In the majority of patients, invasive aspergillosis involves the lungs. Extrapulmonary involvement with total splenic infarction has not been previously described. We illustrate a patient who developed total splenic infarction and septic emboli to the brain from Aspergillus.

AIDS-Related Opportunistic Infections↗