Gluconeogenesis in vitro

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Abstract
A cell-free system prepared from rat liver containing cytosol and mitochondria as well as a number of cofactors at near physiological concentrations formed G-6-P from malate + 3-phosphoglycerate at a rate of 1.11 .+-. 0.09 .mu.mol .cntdot. min-1 .cntdot. g liver-1 (mean .+-. SEM [standard error of the mean], n = 9, 30.degree. C). At least 70% of G-6-P formed was derived from malate as calculated from experiments with [U-14C]malate. The indicated rates were measured between 10 min and 30 min incubation time when the system was near steady state with respect to the lactate/pyruvate ratio and to most of the gluconeogenic intermediates. In the absence of mitochondria, the rate of formation of G-6-P from malate was about 7 times lower than in their presence. A comparison between incubations carried out in presence or absence of mitochondria revealed that mitochondria decreased the lactate/pyruvate ratio and increased the ratio of (ATP + ITP)/(ADP + IDP). Under the present incubation conditions, formation of G-6-P was closely linked to the ratio of (ATP + ITP)/(ADP + IDP) whereas changing redox ratios had little influence on the gluconeogenic rate.