Activities of branched-chain amino acid aminotransferase and branched-chain 2-oxo acid dehydrogenase complex in tissues of maternal and fetal sheep.

Branched-chain amino acid aminotransferase (BCAAT) and branched-chain 2-oxo acid dehydrogenase (BCODH) activities were determined in sheep maternal and fetal liver, kidney, skeletal muscle, adipose and placenta in the fed and 5-day-starved states at 125 days gestation (term is 147 days). BCAAT activities were quite low in maternal skeletal muscle, low in fetal and maternal liver, high in fetal muscle, and very high in placenta. No significant changes occurred with maternal starvation. The high BCAAT activity of the placenta may provide the essential branched-chain 2-oxo acids for the fetus. BCODH activity was highest in liver and kidney of both the mother and fetus; it was largely in the active (dephosphorylated) state in maternal liver and kidney, and in fetal kidney, and about 50% active in fetal liver. The enzyme was largely inactive in fetal muscle, and about 50% active in maternal muscle. Although starvation had little effect on the activity of BCODH in fetal tissues, a significant decrease in activity was observed in maternal tissues, thereby potentially sparing branched-chain amino acids or the corresponding 2-oxo acids for maintenance of the fetus during compromised maternal nutrition.