Catalyzes the reversible deamination of L-leucine to 4-methyl-2-oxopentanoate. H2O + L-leucine + NAD(+) = 4-methyl-2-oxopentanoate + H(+) + NADH + NH4(+) Amino-acid degradation; L-leucine degradation; 4-methyl-2-oxopentanoate from L-leucine (dehydrogenase route): step 1/1. Homohexamer. This enzyme has been successfully altered through several rounds of protein engineering to an enantioselective amine dehydrogenase. Instead of the wild-type alpha-keto acid, the new amine dehydrogenase now accepts the analogous ketone, methyl isobutyl ketone (MIBK), which corresponds to exchange of the carboxy group by a methyl group, to produce chiral (R)-1,3-dimethylbutylamine via a reductive amination reaction. This represents a suitable enzymatic production route for the asymmetric synthesis of amines from prochiral ketones and free ammonia, which is one of the top aspirational reactions challenging the pharmaceutical industry. Belongs to the Glu/Leu/Phe/Val dehydrogenases family.