Activation of branched-chain alpha-ketoacid dehydrogenase complex by alpha-chloroisocaproate in normal and enzyme-deficient fibroblasts.

A method has been developed for the activation of the branched-chain alpha-ketoacid dehydrogenase complex by alpha-chloroisocaproate, an inhibitor of branched-chain alpha-ketoacid dehydrogenase kinase in human cultured skin fibroblasts. The enzyme could be activated by pretreating the cells with alpha-chloroisocaproate before they were disrupted for measurement of the activity. After this treatment, the activity was 2- to 3-fold that of untreated cells (24.8-81.4 pmol/min per mg protein). The enzyme activity in fibroblasts from a patient with maple syrup urine disease was measured by this procedure. After activation by alpha-chloroisocaproate, the activity of fibroblasts from the patient was only 10-14 pmol/min per mg protein (10% of that of controls), and was almost the same as that of the untreated cells from this patient. These results show that it is important to consider the activation state of branched-chain alpha-ketoacid dehydrogenase complex when assaying it in disrupted cells.