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EVIDENCE FOR AN ALTERNATE PATHWAY OF UREA BIOSYNTHESIS

중앙의학 1970년 19권 3호 p.209 ~ 224
김병우,
소속 상세정보
김병우 ( Kim Byung-Woo ) - Yonsei University College of Medicine Seoul Department of Biochemistry

Abstract


Urea biosynthesis and metabolism of L-citrulline 6-14C have been investigated in the isolated perfused rat liver. The rate of urea synthesis from, equimolar , amounts of citrulline and aspartic acid was found to be less than the rate observed with arginine, ammonia, or glutamine at comparable infusion rates. Infusion of ammonium carbonate increased the rate of conversion of L-citrulline 6-14C to urea14C (over the rate observed in the absence of exogenous substrate);an increase in the rate of urea synthesis paralleled the increase in conversion of citrulline to urea. Infusion of glutamine resulted in an increase in the rate of urea synthesis, but this was not accompanied by an increase in the rate, of conversion of labeled citrulline to urea. These results are consistent with the possibility that urea may be formed from glutamine nitrogen without prior conversion of the latter to ammonia.
Citrulline, arginine, and urea were isolated from perfused precancerous livers of rats previously maintained on a diet containing 3-methyl 1-4 dimethylaminoazobenzene. With L-citrulline 6-14C as labeled precursor, the effect-of infusion of various nitrogenous substrates on the specific radioactivity relationships of these compounds was determined. Urea synthesized-in the presence of equimolar amounts of citrulline and aspartic acid had a specific radioactivity identical to that of its immediate. precusor, liver arginine. In the absence of exogenous substrate, the specific radioactivity of urea was about one-half that of liver arginine. In the presence of exogenous ammonia, in the form of ammonium carbo hate, the specific radioactivity of urea was approximately one-quarter that of.

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