Effect of insulin on leucine kinetics in maple syrup urine disease.

Leucine turnover was measured using [1-14C] L-leucine in three patients with classical maple syrup urine disease. There was measurable leucine oxidation although it was lower than in normal adults. Leucine production rate was greater than normal in all three patients with an increased rate of incorporation of leucine into protein and increased protein catabolism. These fluxes were both relatively insensitive to exogenous insulin.