Catalyzes the reversible deamination of L-leucine to 4-methyl-2-oxopentanoate. Exhibits the highest activity with L-leucine as substrate, but can also use other L-amino acids such as L-isoleucine, L-valine and L-2-aminovaleric acid. All of the oxo analogs of the amino acid substrates serve as good substrates for the reverse reaction. H2O + L-leucine + NAD(+) = 4-methyl-2-oxopentanoate + H(+) + NADH + NH4(+) Inhibited by pyridoxal phosphate. Optimum pH is 10.0-10.5 for the oxidative deamination of L-leucine, L-isoleucine and L-valine. Thermostable. Retains full activity on incubation for 10 min at 65 degrees Celsius, but loses about 75% of the activity at 75 degrees Celsius. 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.