Atomic-Resolution Structure of an N(5) Flavin Adduct in D-Arginine Dehydrogenase

D-Arginine dehydrogenase (DADH) catalyzes the flavin-dependent oxidative deamination of D-arginine and other D-amino acids to the corresponding imino adds. The 1.07 angstrom atomic-resolution structure of DADH crystallind with D-leucine unexpectedly revealed a covalent N(5) flavin adduct, instead of the expected iminoleucine product in the active site. This acyl adduct has been successfully reproduced by photoreduction of DADH in the presence of 4-methyl-2-oxopentanoic add (ketoleucine). The iminoleucine may be released readily because of weak interactions in the binding site, in contrast to iminoarginine, converted to ketoleucine, which reacts with activated FAD to form the covalently linked acyl adduct.