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Biomedical subjects

D G Taylor

Publications and source records attributed to D G Taylor.

At least 73 records · Page 4Linked to original sources
PubMed1983

Camphor revisited: involvement of a unique monooxygenase in metabolism of 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid by Pseudomonas putida.

Previously, Pseudomonas putida was shown to degrade (+)-camphor, and cleavage of the first ring of the bicyclic structure involved two monooxygenases (a hydroxylase and a ring oxygen-inserting enzyme), a dehydrogenase, and spontaneous cleavage of an unstable oxygenation product (lactone). Cleavage of the second ring was not demonstrated but was assumed also to occur by ring oxygen insertion, since the predicted oxygenation product was extracted from whole-cell incubation systems. Our investigation established that metabolism of the first ring cleavage intermediate, 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid, occurred through the sequential action of two inducible enzymes, a coenzyme A ester synthetase and an oxygenase. The oxygenase was purified to homogeneity and had a molecular weight of 106,000. This enzyme carried a single molecule of flavin adenine dinucleotide and consisted of two identical subunits. Iron was not present at a significant level. The oxygenase was specific for NADPH as the electron donor and absolutely specific for the coenzyme A ester of 2-oxo-delta 3-4,5,5-trimethylcyclopentenylacetic acid as the substrate. The reaction stoichiometry was compatible with this enzyme being a monooxygenase, and a mass spectral analysis of the methyl ester of the product confirmed the insertion of a single oxygen atom. The enzyme appeared to be analogous to, although distinct from. 2,5-diketocamphane 1,2-monooxygenase in catalyzing a "biological Baeyer-Villiger" reaction with the formation of a lactone. Structural analogy suggested that this lactone, like the first, was also unstable and susceptible to spontaneous ring opening, although this was not experimentally established.

Camphor↗
PubMed1981

The effects of insulin on vasoconstrictor responses in pithed rats.

Pressor responses to spinal sympathetic outflow and selected vasoactive agents were examined in control and diabetic Wistar-Kyoto pithed rats. Diabetes was induced by intravenous injection of alloxan (50 mg/kg). One week after the diabetogen, some of the rats were treated with one daily subcutaneous injection of Lente insulin (2 U/100 Gm) for five weeks. All rats were pithed at six weeks after alloxan. Vasoconstrictor responses to spinal sympathetic outflow, serotonin, norepinephrine, tyramine, and angiotensin were reduced in diabetic rats as compared to their age-matched controls. Administration of insulin caused only partial normalization of these responses. Nondiabetic rats given insulin exhibited vascular responsiveness similar to the treated diabetic group of animals. Blood pressures and heart rates were also found to be similar between the insulin-treated groups and significantly less than control. The finding that insulin does not produce complete normalization of vasoconstrictor responsiveness in diabetic rats may be relevant to the reduced blood pressure observed following insulin treatment.

Animals↗
PubMed1981

A review of the magnetic resonance response of biological tissue and its applicability to the diagnosis of cancer by NMR radiology.

It is now possible to produce cross-sectional NMR images of humans on a routine basis (52-54). Furthermore, there is a growing body of evidence from studies in vitro indicating that cancerous tissue has a significantly different NMR response from healthy tissue. Provided sufficient knowledge of the density, relaxation times, and their interrelation is available, then the technique of NMR radiology may with care be optimized to give considerable improvement over existing techniques in soft tissue discrimination and tumor detection. However, the first-order correlation of relaxation times with water density does raise the question of the uniqueness of diagnosis. Furthermore, the extrapolation of in vitro measurements to the situation in vivo is seen to be complicated by such factors as blood content, muscle and fluid motion, contributions from fat, and fluid in tissue spaces. Considerable study is required in vivo to resolve these uncertainties.

Animals↗
PubMed1980

Cardiovascular effects of alloxan diabetes in normotensive and spontaneously hypertensive rats.

The diabetogenic effects of alloxan (50 mg/kg i.v.) were recorded for 6 weeks in normotensive (WKY) and spontaneously hypertensive (SHR) rats. While systolic blood pressure increased in diabetic WKY, SHR exhibited a reduction in systolic blood pressure over the 6-week period. Heart rate of treated SHR, but not WKY, was reduced significantly during the course of diabetes. 6 weeks postalloxan, the pressor responses to spinal cord stimulation and various vasoactive agents were significantly reduced in both diabetic groups as compared to their age-matched controls. However, in vitro preparations taken from diabetic and control WKY rats showed similar responsiveness to vasoactive agents. The data suggest that circulatory factors contribute to the decreased in vivo responsiveness.

Animals↗
PubMed1978

An inexpensive microcomputer-based stopped-flow data acquisition system.

A low-cost (less than $2,500) microcomputer-controlled data acquisition system for use with a stopped-flow instrument is described. Data acquisition, reduction, signal averaging, kinetic modeling, and plotting are performed under software control. Applications to biological and inorganic systems are presented.

Computers↗
PubMed1978

Screening test for complement activation by counterimmunoelectrophoresis.

This report describes the use of counterimmunoelectrophoresis (CIE) as a method of detecting activation of the complement system. With this technic small amounts of C3 split products (C3c/d) can be detected in plasma samples by specific precipitation with antiserum in less than two hours. The CIE technic is a highly sensitive, rapid method for detecting activation of the complement system in the presence of normal concentrations of C3 measured hemolytically or by radial immunodiffusion (RID) in human disease. A clinical investigation was carried out in 40 patients with systemic rheumatic diseases and 116 normal healthy individuals. The following observations were made: (1) plasmas and sera from normal individuals had normal total complement hemolytic activity (CH50), hemolytic active C4 (C4H50) and C3 (C3H50); (2) in 30% of the serum samples it was possible to identify the presence of C3 split products, in contrast to only 2.5% of the plasma samples obtained simultaneously; (3) in the specimens from patients who had rheumatic disease activity, C3 split products were identified by CIE in all cases except one in the presence of normal C3 protein measured by RID.

Adult↗
PubMed1978

Metabolism of cyclohexane carboxylic acid by Alcaligenes strain W1.

Thirty-three microorganisms capable of growth with cyclohexane carboxylate as the sole source of carbon were isolated from mud, water, and soil samples from the Aberystwyth area. Preliminary screening and whole-cell oxidation studies suggested that, with one exception, all of the strains metabolized the growth substrate by beta-oxidation of the coenzyme A ester. This single distinctive strain, able to oxidize rapidly trans-4-hydroxycyclohexane carboxylate, 4-ketocyclohexane carboxylate, p-hydroxybenzoate, and protocatechuate when grown with cyclohexane carboxylate, was classified as a strain of Alcaligenes and given the number W1. Enzymes capable of converting cyclohexane carboxylate to p-hydroxybenzoate were induced by growth with the alicyclic acid and included the first unambiguous specimen of a cyclohexane carboxylate hydroxylase. Because it is a very fragile protein, attempts to stabilize the cyclohexane carboxylate hydroxylase so that a purification procedure could be developed have consistently failed. In limited studies with crude cell extracts, we found that hydroxylation occurred at the 4 position, probably yielding the trans isomer of 4-hydroxycyclohexane carboxylate. Simultaneous measurement of oxygen consumption and reduced nicotinamide adenine dinucleotide oxidation, coupled with an assessment of reactant stoichiometry, showed the enzyme to be a mixed-function oxygenase. Mass spectral analysis enabled the conversion of cyclohexane carboxylate to p-hydroxybenzoate by cell extracts to be established unequivocally, and all of our data were consistent with the pathway: cyclohexane carboxylate --> trans-4-hydroxycyclohexane carboxylate --> 4-ketocyclohexane carboxylate --> p-hydroxybenzoate. The further metabolism of p-hydroxybenzoate proceeded by meta fission and by the oxidative branch of the 2-hydroxy-4-carboxymuconic semialde-hyde-cleaving pathway.

Alcaligenes↗
PubMed1978

Effects of R-28935 on sympathetic nervous activity in anesthetized cat.

Intravenous administration of erythro-1-(1-[2-(1,4-benzodioxan-2-yl)-2-OH-Et]-4-piperidyl)-2-benzimidazolinone (R-28935) (25--100 microgram/kg) produced a dose-related decrease in spontaneous electrical activity recorded in the splanchnic and renal nerves. Reductions in sympathetic nerve activity were paralleled by hypotension and bradycardia. R 28935-induced depressor responses were not affected by baroreceptor denervation, piperoxan, yohimbine or phentolamine. Results support the idea that R-28935 decreased resting blood pressure and heart rate through a reduction in central sympathetic outflow which does not involve alpha-adrenergic receptor activation.

Animals↗
PubMed1977

Involvement of central GABA receptors in the regulation of blood pressure and heart rate of anesthetized cats.

Intracerebroventricular (i.c.c.) injections of muscimol (0.03-3 microgram/kg) and GABA (30-1000 microgram/kg) caused dose-related reductions in blood pressure and heart rate of anesthetized cats whereas glycine (30-3000 microgram/kg) was much less effective. I.v. administration of muscimol or GABA had little or no effect. Renal sympathetic nerve discharge was also reduced by central GABA receptor stimulation. The effects of both muscimol and GABA were reversed by either picrotoxin or bicuculline administered intravenously. The results suggest an important role for GABA receptors in the central regulation of blood pressure and heart rate.

Aminobutyrates↗
PubMed1977

The purification and properties of p-cresol-(acceptor) oxidoreductase (hydroxylating), a flavocytochrome from Pseudomonas putida.

The enzyme that catalyses the hydroxylation of the methyl group of p-cresol was purified from Pseudomonas putida. It has mol.wt. 115000 and appears to contain two subunits of equal molecular weight. One subunit is a c-type cytochrome and the other is a flavoprotein. Reduction of the cytochrome occurred on addition of substrate. The same enzyme catalyses both p-cresol hydroxylation and the further oxidation of the product, 4-hydroxybenzyl alcohol. The stoicheiometry of acceptor reduced per molecule of substrate oxidized is that for two dehydrogenation reactions. The Km for p-cresol is 7.3 x 10(-6) M and that for 4-hydroxybenzyl alcohol is 47.6 x 10(-6) M. The enzyme, which is assayed with phenazine methosulphate as electron acceptor, was stimulated by particulate material, which probably contains the acceptor in vivo.

Cresols↗