Enzyme and protein turnover in adipose tissue in pregnancy and lactation

1. The relative rates of synthesis of fatty acid synthetase and the pyruvate dehydrogenase complex were measured in adipose tissue in virgin, late pregnant and early lactating rats after injection of L-[2,3-3H]alanine. The relative rate of synthesis of fatty acid synthetase decreased approximately 4-fold between 2 days prepartum and 2 days postpartum. The relative rate of synthesis of the pyruvate dehydrogenase complex did not change. 2. The fractional rate of total adipose tissue protein synthesis was measured by constant infusion with L-[U-14C]tyrosine. Total protein synthesis did not differ in virgin and 2-day lactating rats. The half-life of adipose tissue protein in virgin rats determined by decay of 14C label from protein after injection of NaH14CO3 was 86.9 +/- 6.7 h. This is in close agreement with the half-life (82.5 +/- 20 h) calculated from the fractional rate of protein synthesis determined by the constant infusion method.