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Reactivity of sulphydryl groups of cytosolic and mitochondrial bovine aspartate aminotransferases
Authors:Pasquale Petrilli  Pietro Pucci  Anna Maria Garzillo  Giovanni Sannia  Dr. Gennaro Marino
Affiliation:(1) Istituto di Chimica Organicae Biologica, Università di Napoli, Napoli, Italia;(2) Present address: Istituto di Industrie Agrarie, Università di Napoli, Napoli, Italia;(3) Facoltà di Scienze, Instituto di Chimica Organica e Biologica dell'Università, Via Mezzocannone, 16, 80134 Napoli, Italy
Abstract:
Summary Reactivity of sulphydryl groups of cytosolic and mitochondrial aspartate aminotransferases from ox heart has been studied. A total of 5 and 7 cysteine residues per monomer are present in cAATo and mAATo, respectively. In native conditions only a single sulphydryl group can be titrated by Nbs2 while the catalytic activity remains unchanged, however in the mitochondrial isozyme the reactivity depends on the functional state of the enzyme. Reactivity toward NEM reveals the existence of a syncatalytic sulphydryl group in the cytosolic isozyme. Titration of cAATo with pMB at pH 8 and pH 5 confirms the existence of two exposed sulphydryl groups with a different reactivity. The results compared with those reported on the corresponding isozymes from pig and chicken heart show that syncatalytic sulphydryl groups are of general occurrence in these enzymes.
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