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PMID: 4038255 Published · ppublish English Journal Article Research Support, U.S. Gov't, Non-P.H.S. Research Support, U.S. Gov't, P.H.S.

The apparent Km of ammonia for carbamoyl phosphate synthetase (ammonia) in situ.

The Biochemical journal ·Vol. 229 ·No. 1 ·1985-07-01 ·Pages 205-11

Cohen NS, Kyan FS, Kyan SS, Cheung CW, Raijman L

Abstract

Experiments with carbamoyl phosphate synthetase (ammonia) in solution and in isolated mitochondria are reported which show the following. NH3 rather than NH4+ is the substrate of the enzyme. The apparent Km of NH3 for the purified enzyme is about 38 microM. The apparent Km for NH3 measured in intact isolated mitochondria is about 13 microM. This value was obtained for both coupled and uncoupled mitochondria and was unchanged when the rate of carbamoyl phosphate synthesis was increased 2-fold by incubating uncoupled mitochondria in the presence of 5 mM-N-acetylglutamate. According to the literature, the concentration of NH3 in liver is well below the measured apparent Km. On the basis of this and previous work we conclude that, quantitatively, changes in liver [NH3] and [ornithine] are likely to be the most important factors in the fast regulation of synthesis of carbamoyl phosphate and urea. This conclusion is consistent with all available evidence obtained with isolated mitochondria, isolated hepatocytes, perfused liver and whole animals.

MeSH Terms
Ammonia/metabolism Animals Carbamoyl-Phosphate Synthase (Ammonia)/metabolism Citrulline/biosynthesis Hydrogen-Ion Concentration Kinetics Ligases/metabolism Male Mitochondria, Liver/enzymology Rats Rats, Inbred Strains
Chemicals
Citrulline Ammonia Ligases Carbamoyl-Phosphate Synthase (Ammonia)
Authors & Affiliations
5 authors, click to expand affiliations / ORCID
Cohen N S
Kyan F S
Kyan S S
Cheung C W
Raijman L
References (46)
46 references, click to expand
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Article Info
Journal
The Biochemical journal
Abbr.
Biochem J
ISSN
0264-6021
DOI
10.1042/bj2290205
Published
1985-07-01
Pages
205-11
Language
English
Region
England
NLM ID
2984726R
PMCID
PMC1145168
Subset
IM
Grants
NIGMS NIH HHS · GM 29432 · United States
External Links
PubMed source DOI: 10.1042/bj2290205 PMC Full Text View journal details
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