Identification of two arginase isoenzyme activities along the nephron of Meriones shawi

Conflicting theories on the existence of several renal arginase isoenzymes remain in debate. Because the activity of arginase is high in two embryolog ically different nephron segments of the Meriones shawl kidney, namely the cortical (CPST) and medullary (OSPST) proximal straight tubule and the oute r medullary collecting duct (OMCD), we postulate that these nephron segment s may contain different isoforms. Isolated nephron segments were dissected from collagenase-treated kidneys. Tubules were permeabilized with Triton X- 100 (0.25%) and incubated with increasing Arg concentrations to characteriz e the arginase activity. The results were as follows: (1) in OMCD, one argi nase isoform (E-1), characterized by a high Arg affinity (1.160 mM), was pr esent; (2) in CPST two arginase isoforms were discovered - one, E-1, had a similar K-m (1.407 mM) to that found in OMCD whereas the other (E-2) had a low affinity for Arg (K-m = 18.8 mM); and (3) in OSPST, two isoenzymes were present - E-1 which had a K-m of 1.478 mM and the second isoform that we n amed E-1 which had a K-m of 9.07 mM. In addition, arginase located in CPST and OMCD was strongly inhibited by Orn and Lys. The K-i value for Lys varie d between 1.635 and 2.288 mM. Therefore, this work demonstrates that two ar ginase isoforms are present in the kidney of Meriones shawl. Isoform E-1 is present in the proximal tubule and the collecting duct whereas isoform E-2 is restricted to the proximal tubule.