Pyridoxal 5’-phosphate (PLP)-dependent enzymes have wide catalytic versatility but are rarely known for their ability to react with oxygen to catalyze challenging reactions. Here, using in vitro reconstitution and kinetic anal., we report that the indolmycin biosynthetic enzyme Ind4, from Streptomyces griseus ATCC 12648, is an unprecedented O2- and PLP-dependent enzyme that carries out a four-electron oxidn. of L-arginine, including oxidn. of an unactivated carbon-carbon (C-C) bond. We show that the conjugated product of this reaction, which is susceptible to nonenzymic deamination, is efficiently intercepted and stereospecifically reduced by the partner enzyme Ind5 to give D-4,5-dehydroarginine. Thus, Ind4 couples the redox potential of O2 with the ability of PLP to stabilize anions to efficiently oxidize an unactivated C-C bond, with the subsequent stereochem. inversion by Ind5 preventing off-pathway reactions. Altogether, these results expand our knowledge of the catalytic versatility of PLP-dependent enzymes and enrich the toolbox for oxidative biocatalysis. [on SciFinder(R)]