Immunohistochemical localization of arginase II and other enzymes of arginine metabolism in rat kidney and liver

Arginine is a precursor for the synthesis of urea, polyamines, creatine pho sphate, nitric oxide and proteins. It is synthesized from ornithine by argi ninosuccinate synthetase and argininosuccinate lyase and is degraded by arg inase, which consists of a liver-type (arginase I) and a non-hepatic type ( arginase II). Recently, cDNAs for human and rat arginase II have been isola ted. In this study, immunocytochemical analysis showed that human arginase II expressed in COS-7 cells was localized in the mitochondria. Arginase II mRNA was abundant in the rat small intestine and kidney. In the kidney, arg ininosuccinate synthetase and lyase were immunostained in the cortex, inten sely in proximal tubules and much less intensely in distal tubules. In cont rast, arginase II was stained intensely in the outer stripes of the outer m edulla, presumably in the proximal straight tubules, and in a subpopulation of the proximal tubules in the cortex. Immunostaining of serial sections o f the kidney showed that argininosuccinate synthetase and arginase II were collocalized in a subpopulation of proximal tubules in the cortex, whereas only the synthetase, but not arginase II, was present in another subpopulat ion of proximal tubules. In the liver, all the enzymes of the urea cycle, i .e. carbamylphosphate synthetase I, ornithine transcarbamylase, argininosuc cinate synthetase and lyase and arginase I, showed similar zonation pattern s with staining more intense in periportal hepatocytes than in pericentral hepatocytes, although zonation of ornithine transcarbamylase was much less prominent. The implications of these results are discussed. (C) 1998 Chapma n & Hall.