title: Kinetic studies of the old yellow enzyme. I. The reaction mechanism of the enzyme with reduced nicotinamide adenine dinucleotide.
abstract: The reaction mechanism of old yellow enzyme (NADPH:(acceptor) oxidoreductase, EC 1.6.99.1) was kinetically investigated using NADH as substrate. The enzyme was reduced by NADH via a reaction intermediate which has a specific absorption spectrum. This intermediate decomposed to yield a reduced enzyme and NAD+ through an inrreversible first-order reaction step. The reduced enzyme was reoxidized by oxygen through a second-order reaction process. Individual values of elementary rate constants were measured and a computer simulation of the reaction process was carried out. No involvement of free radical of flavin semiquinone in the reaction process could be shown.
mesh_terms: D000332:Aerobiosis; D003201:Computers; D005292:Ferricyanides / Q000378:metabolism; D005415:Flavins; D005609:Free Radicals; D007700:Kinetics; D008433:Mathematics; D009243:NAD / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D009252:NADPH Dehydrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000201:enzymology
chemical_list: D005292:Ferricyanides; D005415:Flavins; D005609:Free Radicals; D009243:NAD; D009247:NADH, NADPH Oxidoreductases; D009252:NADPH Dehydrogenase