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Biomedical subjects

R G Wilkinson

Publications and source records attributed to R G Wilkinson.

At least 55 records · Page 3Linked to original sources
PubMed1983

Adult stature and age at menarche in Zapotec-speaking communities in the Valley of Oaxaca, Mexico, in a secular perspective.

Adult stature and the age at menarche among individuals from Zapotec-speaking communities in the Valley of Oaxaca in southern Mexico are considered in a secular perspective. Four sets of observations are utilized: 1) adult stature in males and females from five rural communities; 2) age at menarche in adult women and school girls from a single rural community; 3) earlier studies of adult stature in the Valley of Oaxaca; and 4) estimated stature from long bones excavated in various archaeological sites in the Valley of Oaxaca. There were no significant differences among the five communities for stature; hence, the data were pooled for analysis and comparison. Results of linear regression of stature and stature adjusted for the estimated effects of aging after 30 years of age on year of birth indicate negligible secular changes in either sex. Comparisons with statures from earlier surveys, the earliest dates to 1899, also indicate negligible changes. When adult women are grouped according to age, there are no differences in mean ages at menarche between the older and younger women. Mean age at menarche for the total adult sample is 14.53 +/- 0.08 years, which compares favorably with the probit estimate for school girls, 14.70 +/- 0.32 years. These results thus suggest virtually no secular change in adult size and maturity of the Zapotec-speaking population in the Valley of Oaxaca over the past 80 years. Differences in stature between contemporary populations and estimated statures from long bones from several archaeological sites in Oaxaca are small, and thus suggests little secular change over the past one to two-thousand years.

Adult↗
PubMed1983

Partial purification and characterization of two enzymes involved in isovaleric acid synthesis in Clostridium bifermentans.

Conversion of leucine to isovaleric acid by Clostridium bifermentans is achieved by the action of at least two enzymes. One is a transaminase producing alpha-ketoisocaproic acid, which was purified 30-fold from osmotic lysates of late-exponential phase cells by repeated chromatography on DEAE-Sepharose C16B and Sephacryl S300: this represented a 147-fold purification of activity found in sonically disrupted cells. This enzyme had an apparent molecular weight of approximately 190000 and was composed of six identically sized sub-units (molecular weight 31000 +/- 1000). Transamination required pyridoxal phosphate and pyruvate and was optimal at pH 8.6; the apparent Km for leucine was 7.0 mM. Activity was totally inhibited by 1 mM-p-chloromercuribenzoate and partially inhibited by other thiol reagents. The second enzyme decarboxylated alpha-ketoisocaproic acid to form isovaleric acid and was also partially purified by chromatography on DEAE-Sepharose C16B and Sephacryl S300. It has an apparent molecular weight of 240000 and required FAD and coenzyme A for activity; the Km for alpha-ketoisocaproic acid was 4.2 mM and activity was optimal around pH 8.0. This enzyme was a flavoprotein with absorption maxima at 280, 320 and 400 nm, and a fluorescent maximum at 500 nm. The prosthetic group, FAD, dissociated from the protein during purification resulting in an inactive apoenzyme which was only partially re-activated by FAD. Activity was completely inhibited by several thiol reagents tested at 1 mM.

Carboxy-Lyases↗
PubMed1983

Subcellular location of enzymes involved in leucine dissimilation in Clostridium bifermentans.

Conversion of leucine to isovaleric (iV) and isocaproic (iC) acids by cell-free extracts of Clostridium bifermentans was demonstrated using two lysis procedures. Sonication resulted in an extract which had the enzymes to convert leucine to alpha-ketoisocaproic acid (alpha-kiC) and thence iV, but failed to produce iC. Extracts prepared by osmotic lysis, which contained intact membranes, could convert leucine to both iV and iC. The enzyme which converts leucine to alpha-kiC was solubilized during osmotic lysis, whereas the decarboxylase and leucine reductase system remained membrane bound. Osmotic lysis also released at least two small molecular weight, heat-stable, anionic components (3500 greater than molecular weight greater than or equal to 1000), which stimulated decarboxylase activity.

Caproates↗
PubMed1982

Isolation and properties of metronidazole-resistant mutants of Clostridium perfringens.

Clostridium perfringens strains resistant to metronidazole and tinidazole were isolated from the sensitive parent strain CM288 after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Strain CM288 was already resistant to rifampicin and nalidixic acid; these genetic markers helped to confirm the identity of mutants. All mutants showed similar characteristics: they grew more slowly than the parent strain and failed to reach the same maximum turbidity; uptake of metronidazole and tinidazole from culture fluids was slow and end products of glucose metabolism were different from those of the parent. Pyruvate dehydrogenase activity was not detected in broken cell preparations of the mutant strains although this enzyme was readily detected in the parent strain. Changes in end products of glucose metabolism were consistent with the absence of pyruvate dehydrogenase activity because pyruvate was accumulated during growth and lactate levels were higher whereas acetate, CO2 and ethanol levels were diminished.

Clostridium perfringens↗
PubMed1982

Leucine dissimilation to isovaleric and isocaproic acids by cell suspensions of amino acid fermenting anaerobes: the Stickland reaction revisited.

Freshly compared cell suspensions of clostridia (Clostridium bifermentans, C. botulinum proteolytic type A, C. difficile, C. sordellii, and C. sporogenes) and Peptostreptococcus anaerobius converted leucine to isovaleric (iV) and isocaproic (iC) acids in the absence of other amino acids. The optimal pH for conversion was between 8 and 9 at 37 degrees C. The stoichiometry of reaction was compatible with that expected for the Stickland reaction, as the ratio of iV to iC was 1:2, the amount of CO2 produced was equivalent to that of iV, and ammonium ion concentrations were equal to the total C5 and C6 acids formed. The presence of alanine and valine (proton donors in the Stickland reaction) in incubations effectively increased the concentration of iC at the expense of iV production, implying that leucine acted there primarily as a proton acceptor. Glycine and proline (proton acceptors) stimulated both iV and iC production from leucine, but increases in iV concentrations were proportionately greater than for iC so that leucine was primarily a proton donor in the presence of proton acceptors. Glucose stimulated the conversion of leucine to volatile fatty acids but favoured iC production. Production of iC from leucine was inhibited by surface active compounds (cetyltrimethylammonium bromide and desoxycholate) as well as arsenite and iodoacetate. The redox dyes methyl viologen and phenosafranine inhibited iC production more severely than iV production, as did the nitroimidazole antimicrobial agent, metronidazole.

Amino Acids↗
PubMed1979

Isolation and properties of metronidazole-resistant mutants of Bacteroides fragilis.

Metronidazole-resistant mutants of Bacteroides fragilis, isolated after mutagenesis, had diminished ability to take up and metabolize the drug. All the metronidazole-resistant strains had depressed levels of pyruvate dehydrogenase compared with parent cultures. Their end products of glucose metabolism also differed from normal B. fragilis products and were consistent with deficiencies in pyruvate dehydrogenase activity.

Bacteroides fragilis↗
PubMed1978

Purification and properties of beta-lactamase from Bacteroides fragilis.

Beta-Lactamase activity was detected either biologically or using the chromogenic cephalosporin 87/312 in 20 clinical isolates of Bacteroides fragilis with penicillin G minimal inhibitory concentrations of 10 to 100 micrograms/ml. Strain AM78 (minimal inhibitory concentration, greater than 1,000 micrograms/ml) was used to optimize the conditions for production, assay, and storage of the enzyme. The enzymes are cell associated, with less than 1% of activity being found in culture fluids during growth, and can be released from the cell surface by modified osmotic shock procedure. This procedure causes concomitant release of cyclic phosphodiesterase activity. Substrate profiles and the effects of inhibitors were determined for enzymes partially purified by osmotic shock release and gel filtration. The enzymes are cephalosporinases with some penicillinase activity and are inhibited by p-chloromercuribenzoate, cloxacillin, and carbenicillin. The molecular weight, as determined by gel filtration, is 29,000 to 31,000. A method for the purification of the beta-lactamase from strain AM78 is described: the specific activity of the purified enzyme was 3,424 U/mg, about 3,000-fold that of the crude, cell-associated enzyme.

Bacteroides fragilis↗
PubMed1978

Chloramphenicol acetyltransferase of Bacteroides fragilis.

Chloramphenicol-resistant strains of Bacteroides fragilis (minimum inhibitory concentration, 12.5 mug/ml) were isolated from a stool specimen which contained multiply resistant Escherichia coli. The enzyme responsible for resistance, chloramphenicol acetyltransferase, was produced constitutively by these strains; the specific activity was 10-fold lower than that of the E. coli enzymes. Similar activity was not detected in susceptible B. fragilis strains, nor could it be induced by growth in the presence of chloramphenicol or by mutagenesis. The enzyme had a pH optimum of 7.8 and a molecular weight of approximately 89,000. The K(m) for chloramphenicol was 5.2 muM, and the enzyme was sensitive to inhibition by 5,5'-dithiobis-2-nitrobenzoic acid. The enzyme produced by an E. coli strain isolated from the same specimen had a similar K(m) and sensitivity to 5,5'-dithiobis-2-nitrobenzoic acid.

Acetyltransferases↗
PubMed1976

Relationship between hemagglutinin and sialidase from Clostridium perfringens CN3870: chromatographic characterization of the biologically active proteins.

Biochemical characterization of hemagglutinin and sialidase activities from Clostridium perfringens strain CN3870 revealed that this strain produced three sialidase enzymes that were separable to gel filtration, ion exchange chromatography, and polyacrylamide gel electrophoresis. The molecular weights of sialidase I, II, and III activities were 310,000 +/- 10,000, 105,000 +/- 4,000 and 64,000 +/- 2,000, respectively, the first figure being an approximate value only.

Agglutinins↗
PubMed1976

Relationship between hemagglutinin and sialidase from Clostridium perfringens CN3870: gel filtration of mutant and reverant activities.

Gel filtration of supernatant fluids, from the wild-type Clostridium perfringens, strain CN3870, and several of the mutants and reverants derived from this strain, showed that these mutants failed to product detectable amounts of still produced sialidase III activity. The reverants tested had regained the ability to produce approximately wild-type levels of the I and II forms of both activities. These results showthat there is a direct relationship between the production of the I form and hemagglutinin and sialidase activities and the production of the II form of these biologically active proteins. Models that explain the genetic basis for these results are discussed.

Agglutinins↗
PubMed1975

Isolation and characterization of Clostridium perfringens mutants altered in both hemagglutinin and sialidase production.

The relationship between the production of hemagglutinin and sialidase activities by Clostridium perfringens was investigated by screening for mutants producing reduced levels of hemagglutinin activity. Twelve mutants were isolated; all produced reduced levels of sialidase activity and several had other altered phenotypic markers. Revertants that regained the ability to produce active hemagglutinin were isolated. All of these revertants produced increased sialidase activity. These results show that the production of hemagglutinin activity is directly related to the production of sialidase activity. Evidence is also presented that the processes of sporulation and the production of extracellular proteins are interrelated.

Agglutinins↗