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Biomedical subjects

H D Brown

Publications and source records attributed to H D Brown.

At least 55 records · Page 3Linked to original sources
PubMed1975

Biosynthesis of branched-chain amino acids in yeast: effect of carbon source on leucine biosynthetic enzymes.

The three enzymes in the leucine biosynthetic pathway of yeast do not exhibit coordinate repression and derepression in response to the carbon source available in the culture medium. Growth in an acetate medium results in derepression of the first enzyme in the pathway, alpha-isopropylmalate synthase, and repression of the second two enzymes, alpha-isopropylmalate isomerase and beta-isopropylmalate dehydrogenase, relative to the levels found in glucose-grown cells. The role of endogenous leucine pools as a mediator of these differences was investigated. The leucine pools did not differ significantly between acetate-grown and glucose-grown cells. However, an elevated endogenous leucine pool, caused by exogenous leucine in the growth medium, did decrease the rate of decay of alpha-isopropylmalate synthase activity observed when acetate-grown cells were shifted to glucose. Evidence is provided suggesting that an elevated endogenous leucine pool may increase the in vivo stability of alpha-isopropylmalate synthase under several different conditions. Studies on the kinetics of alpha-isopropylmalate synthase decay in vivo and sensitivity to leucine inhibition indicate that there are two classes of the enzyme in acetate-grown yeast cells.

Acetates↗
PubMed1975

Preparation and properties of matrix-supported horseradish peroxidase.

A new method of enzyme immobilization has been described using poly(4-methacryloxybenzoic acid) as the carrier. Activation of the polymer, prior to enzyme attachment, was achieved with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline. The enzyme coupling step proceeded through nucleophilic attack by the protein on a mixed carbonic anhydride. The degree of polymer activation was determined by analysis for quinoline, a by-product of the reaction. The polymer-enzyme complex was compared to the enzyme in solution in terms of pH optimum, substrate kinetics, and thermal denaturation. Potential uses of the polymerenzyme system in chemical synthesis of benzoquinone derivatives are discussed.

Aniline Compounds↗
PubMed1975

Preliminary studies on the metabolism of 3,2'-dimethyl-4-aminobiphenyl in the rat.

Distribution of 3,2-dimethyl-4-aminobiphenyl (DMAB) and its metabolites in vivo and the metabolism of DMAB by liver in vitro have been studied in the Wistar rat. DMAB-HCI purified by recrystallization and dissolved in ethanol was injected subcutaneously and extractions made from liver, feces, and urine. Similar technical procedures were used to study in vitro metabolism in rat liver homogenates. Two components were isolated from urine and liver having Rf values (thin-layer chromatography) of 0.13 and 0.59, respectively. Three additional metabolites were found in the hydrolyzed fecal fraction. Rechromatography of the major fecal component yielded 6 fluorescent compounds. Gas-liquid chromatography of the most highly fluorescent of these indicated at least 3 additional metabolites. The evidence presented indicates that the liver transforms DMAB to several metabolites which are rapidly transferred in conjugated form to the intestine via the bile. The urine does not appear to be the major excretory route. We have examined the purity of commercially available DMAB free base and DMAB-HCL and found an impurity that comprises approximately 10-24% of the total samle upon GLC analysis, depending upon the supplier. This contaminant was completely removed by recrystallization of the hydrochloride and the chemical identity of purified compound as DMAB confirmed. Recommendations are presented for the use of this purified compound in a biological system.

Aminobiphenyl Compounds↗
PubMed1972

Further studies of electron transport components in a series of Morris hepatoma-bearing rats.

Microsomal electron transport components (NADPH oxidase, NADPH-ferricyanide reductase, cytochromes P-450 and b(5)) have been studied in Buffalostrain rat liver and in a series of Morris hepatomata (9618A-2, 7800, 7795 and 7787). Normal liver values differed significantly from those measured in livers of tumourbearing animals. In all hepatomata per se, very low levels were found.

Animals↗