Stereochemistry and accessibility of prosthetic groups in flavoproteins.

Using 8-demethyl-8-hydroxy-5-deaza-5-carba analogues of the appropriate flavin nucleotides, we determined the stereochemistry of interaction between coenzyme and substrate for several flavoproteins. The enzymes were D-amino acid oxidase, L-lactate oxidase, and D-lactate dehydrogenase, all three of which interact with pyruvate, as well as cyclohexanone monooxygenase and 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase, which were both probed with nicotinamide nucleotides. L-Lactate oxidase and D-lactate dehydrogenase used the si face of the modified flavin ring while the other three enzymes showed re-side specificity. This selection of flavoenzymes includes FAD- and FMN-dependent enzymes, enzymes that follow a carbanion mechanism, and others that have hydride transfer as an integral part of their reaction pathway.