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Biosynthesis of agmatine in isolated mitochondria and perfused rat liver: studies with (15)N-labelled arginine

By Oksana Horyn, Bohdan Luhovyy, Adam Lazarow, Yevgeny Daikhin, Ilana Nissim, Marc Yudkoff and Itzhak Nissim

Abstract

An important but unresolved question is whether mammalian mitochondria metabolize arginine to agmatine by the ADC (arginine decarboxylase) reaction. (15)N-labelled arginine was used as a precursor to address this question and to determine the flux through the ADC reaction in isolated mitochondria obtained from rat liver. In addition, liver perfusion system was used to examine a possible action of insulin, glucagon or cAMP on a flux through the ADC reaction. In mitochondria and liver perfusion, (15)N-labelled agmatine was generated from external (15)N-labelled arginine. The production of (15)N-labelled agmatine was time- and dose-dependent. The time-course of [U-(15)N(4)]agmatine formation from 2 mM [U-(15)N(4)]arginine was best fitted to a one-phase exponential curve with a production rate of approx. 29 pmol·min(−1)·(mg of protein)(−1). Experiments with an increasing concentration (0– 40 mM) of [guanidino-(15)N(2)]arginine showed a Michaelis constant K(m) for arginine of 46 mM and a V(max) of 3.7 nmol·min(−1)·(mg of protein)(−1) for flux through the ADC reaction. Experiments with broken mitochondria showed little changes in V(max) or K(m) values, suggesting that mitochondrial arginine uptake had little effect on the observed V(max) or K(m) values. Experiments with liver perfusion demonstrated that over 95% of the effluent agmatine was derived from perfusate [guanidino-(15)N(2)]arginine regardless of the experimental condition. However, the output of (15)N-labelled agmatine (nmol·min(−1)·g(−1)) increased by approx. 2-fold (P<0.05) in perfusions with cAMP. The findings of the present study provide compelling evidence that mitochondrial ADC is present in the rat liver, and suggest that cAMP may stimulate flux through this pathway

Topics: Research Article
Publisher: Portland Press Ltd.
Year: 2005
DOI identifier: 10.1042/BJ20041260
OAI identifier: oai:pubmedcentral.nih.gov:1138948
Provided by: PubMed Central
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