7 Flavoprotein Oxidases

Abstract

The concept of a flavoprotein oxidase is easier to understand than to define by international rules. A flavoprotein or flavoenzyme is commonly understood to mean an apoenzyme which together with its more or less tightly attached flavin coenzyme, catalyzes a redox reaction during which either one or two electrons from the electron donor are transferred transiently to the isoalloxazine nucleus of the flavin coenzyme and then to the electron acceptor. All flavoproteins belong to the class oxidoreductases. The term “oxidase” is a recommended name for an oxidoreductase which utilizes O2 as the electron acceptor. A flavoprotein oxidase is defined as a flavoprotein. The definition singles out the simple flavoprotein oxidases in which flavin are the only recognizable prosthetic group that transiently accepts electrons originating in the donor substrate. The emphasis of this chapter concerns the kinetic and chemical mechanism of flavoprotein oxidase catalysis. There are several cogent reasons for such relatively restricted coverage. In the case of flavin, recent advances in the understanding of the mechanism of both the enzymic and nonenzymic reactions have resulted in a most productive liaison between the two approaches. In addition, this chapter discusses enzymological and model studies related to the mechanism of action of only three flavoprotein oxidases—namely, glucose oxidase, L-amino acid oxidase, and D-amino acid oxidase.