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Biomedical subjects

B Davis

Publications and source records attributed to B Davis.

At least 289 records · Page 16Linked to original sources
PubMed1973

Malate dehydrogenase isoenzymes in division synchronized cultures of euglena.

Sucrose density gradient centrifugation of broken cell suspensions of autotrophically grown Euglena gracilis Klebs. has allowed the separation of chloroplasts, mitochondria, and peroxisomes. Chlorophyll was taken as a marker for chloroplasts, fumarase and succinate dehydrogenase for mitochondria, and glycolate oxidoreductase for peroxisomes. Peaks of malate dehydrogenase (l-malate-NAD oxidoreductase, EC 1.1.1.37) activity were found in the mitochondrial and peroxisomal fractions. Acrylamide gel electrophoresis showed specific isoenzymes in the mitochondrial and peroxisomal fractions and a third isoenzyme in the supernatant. The mitochondrial isoenzyme which had a Km (oxaloacetate) of 30mum was inhibited by oxaloacetate concentrations above 0.17 mm, an inhibition of 50% being given by 0.9 mm oxaloacetate. The peroxisomal isoenzyme had a Km (oxaloacetate) of 24 mum, was inhibited by oxaloacetate concentrations above 0.13 mm, 50% inhibition being given by 0.25 mm oxaloacetate. Malate dehydrogenase activity in the supernatant did not show inhibition by increasing oxaloacetate concentration, the Km (oxaloacetate) being 91 mum.In division synchronized cultures of Euglena, all three isoenzymes of malate dehydrogenase were synthesized over the light phase of the cycle. Darkening light phase cultures did not affect malate dehydrogenase activity. The addition to cultures of cycloheximide at a concentration previously shown to inhibit protein synthesis on Euglena cytoplasmic ribosomes completely inhibited increase in malate dehydrogenase activity over the cell cycle. Malate dehydrogenase activity was unaffected by the addition of chloramphenicol in amounts known to inhibit preferentially protein synthesis on 70S ribosomes.

Journal Article↗
PubMed1972

Insulin release from mouse islets. Effect of glucose and hormones on adenylate cyclase.

The adenylate cyclase system of normal mouse islets was characterized. The pH optimum of the system was 7.6. The enzyme preparation contained particulate phosphodiesterase activity. This could be removed by treatment with 0.4% (v/v) Triton X-100 or inhibited by 8mm-theophylline in the presence of 2mm-cyclic AMP (adenosine 3':5'-cyclic monophosphate). ATP at 0.32mm produced one-half maximal enzyme activity. The enzyme was stimulated in the presence of F(-) and strongly inhibited by Ca(2+). The isolated enzyme retained hormonal sensitivity and was stimulated by glucagon, pancreozymin and secretin at physiological concentrations. Glucose at 17mm, 8mm and 2mm had no direct effect on the activity of the enzyme; neither did galactose at the same concentrations. Groups of islets incubated in 17mm- or 2mm-glucose for 5 or 15min and then homogenized and assayed for adenylate cyclase activity showed no differences in adenylate cyclase activity. The results suggest that the mechanism of glucose-mediated insulin release is not via the adenylate cyclase system. Hormones, however, could mediate insulin secretion via their effects on the adenylate cyclase system.

Adenylyl Cyclase Inhibitors↗
PubMed1972

Anaesthetic, cardiovascular and respiratory effects of a new steroidal agent CT 1341: a comparison with other intravenous anaesthetic drugs in the unrestrained cat.

1. The anaesthetic, cardiovascular, respiratory and adverse effects produced by the intravenous injection of CT 1341, thiopentone, methohexitone, pentobarbitone, propanidid and ketamine have been compared in unrestrained cats prepared with chronically implanted venous and arterial cannulae. Aortic blood pressure and heart rates were monitored before, during and after loss of consciousness.2. CT 1341 produced rapid induction of anaesthesia followed by moderately rapid recovery, was active over a wide range of doses and caused minimal respiratory depression and few adverse effects. It caused an initial short-lasting tachycardia and fall in aortic blood pressure succeeded by a secondary depressor response.3. The safety margin was narrower with the barbiturate drugs than with CT 1341, and large doses induced apnoea and respiratory depression. Small doses of methohexitone elicited excitatory effects and large doses caused severe respiratory and circulatory depression, and recovery from anaesthesia was protracted.4. Propanidid induced short-lasting light anaesthesia. The safety margin was narrowest with this drug and induction was associated with adverse circulatory, respiratory and other effects.5. Ketamine was active over a wide range of doses but exhibited qualitatively different properties from the other anaesthetics. Induction was slower after small doses and these produced circulatory stimulation, catatonia and bizarre behavioural effects. Large doses caused respiratory and circulatory depression and recovery was protracted.6. It is concluded that CT 1341 has a wider therapeutic latitude, produces less respiratory depression and has other advantages over the currently used intravenous anaesthetics.

Anesthesia, Intravenous↗
PubMed1969

Gram-negative bacilli in burns.

In a period of two years, 865 strains of Gram-negative bacilli other than Pseudomonas aeruginosa isolated from burns were identified by a range of tests. The commonest species were Proteus mirabilis, Escherichia coli, and Enterobacter cloacae. Many strains of Klebsiella aerogenes, Enterobacter aerogenes, and Bacterium anitratum were also found.A large proportion of the strains were tested for sensitivity to nalidixic acid, ampicillin, kanamycin, chloramphenicol, tetracycline, and carbenicillin, and smaller numbers of strains were tested for sensitivity to cephaloridine, polymyxin, streptomycin, sulphadiazine, sulfamylon, and trimethoprim. The proportion of strains sensitive and resistant to different antibacterial agents varied widely with species of bacteria. A large proportion of the strains of E. coli and P. mirabilis were resistant to ampicillin, which was much used in treatment; resistance appeared least often towards nalidixic acid, kanamycin, trimethoprim, and gentamicin. Multiple resistance occurred less often among strains of E. coli than among Klebsiella spp, Enterobacter spp, and P. mirabilis. Phage and serological typing of Ps. aeruginosa showed that most infections of burns with this organism were due to strains previously found in other patients in the same ward. Taken with other evidence, this supported the view that most infections with Ps. aeruginosa were not acquired from the patient's own flora but from sources in the hospital environment.

Anti-Bacterial Agents↗