Developmental changes in the enzymatic capacity for reduction and oxidation of alpha-ketoadipate in rat liver, heart, kidney, and brain.

alpha-Ketoadipate, an intermediate common to lysine and tryptophan metabolism, is a substrate for both alpha-ketoadipate reductase (alpha-KAR) and alpha-ketoadipate dehydrogenase (alpha-KADH). A comparison was made of the activities of these two enzymes in liver, heart, kidney, and brain of rats during the period from 5 days before birth to 56 days after birth. In general, both enzymes increased in activity during development in all tissues tested; however, different patterns of increase were observed (Figs. 1 and 2). The ratio of alpha-KADH to alpha-KAR (on the basis of activity/g tissue) did not change significantly in liver until day 10 and then increased 6.6-fold (from 0.08 to 0.53) in the period from day 10 to day 28. For other tissues the ratios increased 5.5-fold in hearts (from 0.2 to 1.1), 12-fold in kidney (from 0.2 to 2.4), and 5.3-fold in brain (from 0.3 to 1.6) during the period from day -5 to day 56. These results suggest that alpha-KAR has a major role in the metabolism of lysine and tryptophan during development.