Impact of nutrition on postnatal development of serine-threonine dehydratase and branched-chain keto acid dehydrogenase in the rat.

The developmental patterns of two amino acid-catabolizing enzymes, serine-threonine dehydratase (STD) and branched-chain alpha-keto acid dehydrogenase (BCKAD), were investigated in growing rats. At 10, 15, 20, 30, and 60 days of age, STD and BCKAD activities were determined in pup tissues. Hepatic STD activity increased more than 3-fold between 10 and 20 days of age; after this peak, activity decreased by 30 days of age. Threonine dosing did not affect STD activity at any age. In the liver, kidney, brain and skeletal muscle, total BCKAD activity increased 2- to 4-fold between 10 and 30 days of age. Percentages of BCKAD active in all tissues decreased between 10 and 15 days of age, associated with a large increase in total activity. The percentages of BCKAD activity were unchanged between 20 and 30 days of age but increased from 30 to 60 days of age, associated with a decrease in total activity. Leucine dosing did not affect total BCKAD activity at any age. These results demonstrate that both STD and BCKAD develop late during the suckling period and total activities are unresponsive to excess dietary amino acids.