ISOLATION AND CHARACTERIZATION OF THE FLAVIN-BINDING DOMAIN OF FLAVOCYTOCHROME B(2) EXPRESSED INDEPENDENTLY IN ESCHERICHIA-COLI

Flavocytochrome b(2) consists of two distinct domains. The N-terminal domain contains protohaem IX and the larger, C-terminal domain contain s flavin mononucleotide (FMN). We describe here the isolation of the f lavin-binding domain expressed in Escherichia coli independent of the cytochrome domain. The isolated domain is an efficient lactate dehydro genase with ferricyanide as electron acceptor but reduces cytochrome c , the physiological oxidant for flavocytochrome b(2), extremely poorly ; electron transfer from the flavin-binding domain to the separately e xpressed cytochrome domain is undetectable. FMN reduction by lactate o ccurs as a single exponential process in the isolated flavin-binding d omain, in contrast to the biphasic kinetics observed with native flavo cytochrome b(2).