Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.3 (collagenase)
 18,340 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat kidneys extract citrulline derived from the intestinal metabolism of glutamine and convert it stoichiometrically into arginine. This pathway constitutes the major endogenous source of arginine. We investigated the localization of enzymes of arginine synthesis, argininosuccinate synthase and lyase, and of breakdown, arginase and ornithine aminotransferase, in five regions of rat kidney, in cortical tubule fractions and in subcellular fractions of cortex. Argininosuccinate synthase and lyase were found almost exclusively in cortex. Arginase and ornithine aminotransferase were found in inner cortex and outer medulla. Since cortical tissue primarily consists of proximal convoluted and straight tubules, distal tubules and glomeruli, we prepared cortical tubule fragments by collagenase digestion of cortices and fractionated them on a Percoll gradient. Argininosuccinate synthase and lyase were found to be markedly enriched in proximal convoluted tubules, whereas less than 10% of arginase and ornithine aminotransferase, were recovered in this fraction. Arginine production from citrulline was also enriched in proximal convoluted tubules. Subcellular fractionation of kidney cortex revealed that argininosuccinate synthase and lyase are cytosolic. We therefore conclude that arginine synthesis occurs in the cytoplasm of the cells of the proximal convoluted tubule.
 ...
PMID:Cellular and subcellular localization of enzymes of arginine metabolism in rat kidney. 131 26

1. Arginine is essential for growth in the kitten and, because of the resulting hyperammonaemia, in the adult cat an arginine-free diet is life threatening. 2. The kidney is the main site of arginine synthesis. 3. This study was performed to determine whether the cat kidney synthesizes arginine and to establish which factors, such as low citrullinaemia, defects of argininosuccinate synthase and lyase activities or high renal arginase activity, might limit renal arginine production. 4. Identified nephron segments were isolated by microdissection from collagenase-treated cat kidney. 5. Arginine metabolism was studied by incubating the nephron segments with either physiological concentrations of L-[ureido-14C]citrulline (anabolism) or L-[guanido-14C]-arginine (catabolism). Arginine and urea were measured by a micro-enzymatic method. Amino acids were measured by HPLC. 6. In cat blood, the citrulline, but not the arginine, concentration was very low by comparison with other species. 7. Arginine synthesis occurred almost entirely in the proximal tubule, the highest rate occurring in the proximal convoluted tubule and the lowest in the medullary straight proximal tubule. 8. Arginase activity was restricted to the proximal tubule. Urea production increased from the convoluted towards the medullary straight tubule. 9. The limited capacity of the cat kidney to produce arginine in vivo may result from the low blood concentration of citrulline and from the high arginase activity in the various proximal cells with the ability to synthesize arginine.
 ...
PMID:Arginine metabolism in cat kidney. 886 70