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Biomedical subjects

B A Orsi

Publications and source records attributed to B A Orsi.

At least 19 recordsLinked to original sources
PubMed1989

Nitroreductase activity of NADH dehydrogenase of the respiratory redox chain.

1. An NADH-dependent nitroreductase from the inner membrane of ox liver mitochondria copurified with Complex I of the respiratory redox chain (NADH:ubiquinone oxidoreductase, EC 1.6.5.3). 2. The corresponding nitroreductase from ox heart mitochondria co-purified with the NADH-cytochrome c reductase of Mahler, Sarkar & Vernon [(1952) J. Biol. Chem. 199, 585-597] [NADH: (acceptor) oxidoreductase, EC 1.6.99.3], a component of Complex I that contains the FMN. 3. The mitochondrial nitroreductase activity is attributed to the flavoprotein component of Complex I.

Animals↗
PubMed1982

The slow kinetic transients of arylsulphatase A.

A simple model is described to account for the anomalous time course of arylsulphatase A. In the case of the ox liver and human placental enzymes the enzyme-nitrocatechol sulphate complex can, in addition to forming products, slowly break down to form an inactive species which can turn in slowly regenerate active enzyme. When the inactive form binds sulphate the rate of reactivation is enhanced, 218-fold in the case of the ox enzyme. Rat liver arylsulphatase A is refractory to reactivation by sulphate.

Animals↗
PubMed1979

Kinetic mechanism of the aliphatic amidase from Pseudomonas aeruginosa.

The kinetic constants for hydrolysis and transfer (with hydroxylamine as the alternate acceptor) of the aliphatic amidase (acylamide amidohydrolase, EC 3.5.1.4) from Pseudomonas aeruginosa were determined for a variety of acetyl and propionyl derivatives. The results obtained were consistent with a ping-pong or substitution mechanism. Product inhibition, which was pH dependent, implicated an acyl-enzyme compound as a compulsory intermediate and indicated that ammonia combined additionally with the free enzyme in a dead-end manner. The uncompetitive activation of acetamide hydrolysis by hydroxylamine and the observation that the partitioning of products between acetic acid and acetohydroxamate was linearly dependent on the hydroxylamine concentration substantiated these conclusions and indicated that deacylation was at least partially rate limiting. With propionamide as the acyl donor apparently anomalous results, which included inequalities in certain kinetic constants and a hyperbolic dependence of the partition ratio on the hydroxylamine concentration, could be explained by postulating a compulsory isomerisation of the acyl-enzyme intermediate prior to the transfer reaction.

Acetamides↗