Metabolic processes in cytoplasmic particles of the avocado fruit. VII. Oxidative and phosphorylative activities throughout the climacteric cycle.

Abstract

Cytoplasmic particles (mitochondria) showing dependence of oxidation on ADP were isolated from avocado fruit at 4 stages of ripening, "early" and "late" preclimacteric, climacteric and postclimacteric. In order to obtain respiratory control, it was essential to homogenize the tissue and to assay the mitochondrial preparation in the presence of bovine serum albumin in addition to other addenda used normally. The particles displayed a basic ability to oxidize succinate, malate, and a-ketoglutarate. Succinate was oxidized by particles from fruit at all ripening stages at about the same rate. With malate there appeared to be a block in the oxidation at the preclimacteric stage and a progressive inhibition of the oxidation rates at the climacteric and post-climacteric stages. Both these points of inhibition were overcome by thiamine pyrophosphate addition, suggesting an involvement of oxaloacetate in the mechanism. Oxidation of [alpha]-ketoglutarate required the addition of thiamine pyrophosphate only with particles from preclimacteric fruit. In general, respiratory control ratios increased with ripening, as did the ADP to oxygen uptake values. Indications are that a cofactor requirement could form a regulatory mechanism and act as a contributory factor in the climacteric rise.