CYTOSOLIC NAD(-CELLS() CONTENT STRICTLY DEPENDS ON ATP CONCENTRATION IN ISOLATED LIVER)

By focusing on the question of the thermodynamic relationships involve d in the regulation of biological energy conversion, bioenergetic stud ies usually consider the free pyridine and adenine nucleotide rather t han their total pools, in either cytosol or mitochondria. In this stud y, we report a new observation that, at steady state, nicotinamide nuc leotide content is increased by a rise in the ATP content of the whole cell under physiological conditions. It is a straight line relationsh ip when only NAD(+) and ATP are considered, When regarding the compart mentation of this phenomenon, it appears that the linear relationship between [NAD(+)] and [ATP] occurs only in the cytosol. Such a dependen ce could be a supplementary mechanism of regulation between various me tabolic pathways in the liver cell. (C) 1997 Federation of European Bi ochemical Societies.