Distribution of two aminotransferases and D-amino acid oxidase within the nephron of young and adult rats.

In the adult rat kidney, alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.1) and D-amino acid oxidase (EC 1.4.3.3) were measured in glomeruli, 4 parts of the proximal tubule, 2 parts of the distal tubule and in patches from the thin limb area and the papilla. These enzymes were measured in more limited parts of the nephron during postnatal development. Adult aspartate aminotransferase activities (percentage of the highest) ranged from 100 in the distal straight segment to 25 in the late part of the proximal straight segment to 10 in the thin limb and papillary area. Alanine aminotransferase (lower by a factor of 100 in absolute terms) was distributed as the mirror image of aspartate aminotransferase within proximal and distal tubules. D-Amino acid oxidase was 850-fold higher in proximal straight segments than in medullary structures. During development alanine aminotransferase increased 6-fold and D-amino acid oxidase, 4.5-fold in proximal straight tubules but aspartate aminotransferase increased in distal straight tubles 8-fold.