The Role of Mitochondrially Bound Arginase in the Regulation of Urea Synthesis

Abstract

The main goal of the current study was to elucidate the role of mitochondrial arginine metabolism in the regulation of N-acetylglutamate and urea synthesis. We hypothesized that arginine catabolism via mitochondrially bound arginase augments ureagenesis by supplying ornithine for net synthesis of citrulline, glutamate,

3-Isobutylmethylxanthine Inhibits Hepatic Urea Synthesis

“…The concentration and isotopic enrichment in NAG in liver or mitochondrial extracts were determined using GC-MS and isotope dilution (5,19). The formation of NAG isotopomers was monitored using ions at m/z 158, 159, 160, 161, 162 and 163, for M ϩ 1, M ϩ2, M ϩ 3, M ϩ 4, and M ϩ 5 (containing 1-5 13 C atoms), respectively.…”

“…The formation of NAG isotopomers was monitored using ions at m/z 158, 159, 160, 161, 162 and 163, for M ϩ 1, M ϩ2, M ϩ 3, M ϩ 4, and M ϩ 5 (containing 1-5 13 C atoms), respectively. In experiments with isolated mitochondria, the production of 15 N-labeled NAG and citrulline from 15 N-labeled precursors was determined as described (5,19).…”

“…For measurement of 13 C or 15 N enrichment in amino acids or urea, the liver extract or effluent samples were prepared as described previously (5,19). 15 N enrichment in effluent ammonia was determined as in Ref.…”

“…Mitochondria were isolated from the liver of overnight fasted rats by differential centrifugation as described previously (5,19). Respiratory control and oxygen consumption were determined (5,6,19).…”

“…To address these questions, experiments were carried out with either a liver perfusion system or isolated mitochondria. We used 15 N-labeled ammonia or [5-15 N]glutamine to assess the production of NAG and CP and thus the rates of urea formation (5,18,19). Because the process of urea synthesis involves equimolar consumption of NH 4 ϩ and aspartate-N, and because glutamine is a major source of ammonia and aspartate-N for urea synthesis (16 -18), the use of [5-15 N]glutamine was meant to determine in liver perfusion the rate of ureagenesis in a physiological setting, as demonstrated previously (4,17,18 15 N]citrulline was used as a proxy for the production of CP, and thus, activity of CPS-I as indicated previously (8 -12).…”