Catalyzes the reversible deamination of L-leucine to 4-methyl-2-oxopentanoate. Can also use other substrates such as L-isoleucine, L-valine and L-2-aminobutyrate. The 2-oxo analogs of branched-chain and straight-chain amino acids serve as good substrates for the reverse reaction. H2O + L-leucine + NAD(+) = 4-methyl-2-oxopentanoate + H(+) + NADH + NH4(+) Optimum pH is 10.3 for the oxidative deamination of L-leucine. Thermostable. Retains full activity on heating at 65 degrees Celsius for 1 hour, but loses the activity completely on heating at 70 degrees Celsius for 1 hour. Amino-acid degradation; L-leucine degradation; 4-methyl-2-oxopentanoate from L-leucine (dehydrogenase route): step 1/1. Homooctamer. Belongs to the Glu/Leu/Phe/Val dehydrogenases family.