FLAVOCYTOCHROME-B2

This chapter describes flavocytochrome b2 that is a soluble component of the intermembrane space of yeast mitochondria, where it catalyzes the oxidation of L-lactate to pyruvate with subsequent transfer of electrons to cytochrome c. The enzyme is a tetramer of identical subunits, with each subunit containing both flavin mononucleotide (FMN) and protoheme IX prosthetic groups in two functionally distinct domains. A short electron transport chain involving flavocytochrome b2, cytochrome c, and cytochrome c oxidase allows yeast to respire on L-lactate, even if the main electron transport chain is blocked—for example, by antimycin. The two flavocytochromes b2 that have been characterized to date—namely, from Hemimysis anomala and Saccharomyce cerevisiae—have undergone consider able divergence but retain 60% sequence identity. As both genes have been isolated and sequenced, it is possible to engineer hybrid enzymes in which part of one flavocytochrome b2 is substituted by the corresponding region from the enzyme from the other species. © 1991 Academic Press, Inc.