Branched chain amino acid transaminase and branched chain alpha-ketoacid dehydrogenase activity in the brain, liver and skeletal muscle of acute hepatic failure rats.

Branched chain amino acid (BCAA) transaminase activity increased in both the mitochondrial and supernatant fractions of brain from hepatic failure rats, in which a partial hepatectomy was performed 24h following carbon tetrachloride (CCl4) administration, although the activity of liver and skeletal muscle was the same as in control rats. The elevation of mitochondrial BCAA transaminase activity in liver-injured rats was partly due to increased activity of brain specific Type III isozyme. Branched chain alpha-ketoacid (BCKA) dehydrogenase in the brain homogenates was not significantly altered in acute hepatic failure rats, while the liver enzyme activity was markedly diminished. BCKA dehydrogenase activity in the brain homogenates was inhibited by adding ATP to the assay system, and was activated in vitro by preincubating the brain homogenate at 37 degrees C for 15 min. These findings suggest that brain BCAA catabolism is accelerated in acute hepatic failure rats.