Fatty acid-binding protein, a potential regulator of energy production in the heart. Investigation of mechanisms by electron spin resonance.

The catabolic system, translocating then beta-oxidizing fatty acids in the mitochondria and considered as the major energy generator in the heart, was shown in the present study to be strongly regulated by fatty acid-binding protein (FABP), a self-aggregated and exclusive protein for the binding and transport of fatty acids in the cardiac cell cytoplasm. The mechanism behind this regulation was investigated by using new techniques in this field: i.e. electron spin resonance (ESR) and spin-labeling for the simultaneous analysis of partitioning and beta-oxidation of fatty acids in the isolated cardiac mitochondria. The step of this catabolic system which is controlled by FABP was shown to be the acylcarnitine transfer into the mitochondria. Two of the multi-self-aggregated FABP molecular species, namely those existing at FABP concentrations around 1.1 and 2.2 g.liter-1, were found to act as specific translocators delivering acylcarnitine to the mitochondrial beta-oxidative system. The energy production in the heart might thus be critically dependent on optimized FABP concentrations in the cardiac cells.