Stimulations of Oxygen Uptake by Electron Transfer Inhibitors

Abstract

The rates of oxidation of endogenous substrates and of p32 incorporation into soluble esters were studied in tissue slices of avocado (Persea gratissima, Gaertn.) fruit. The inhibitors of cyto-chrome oxldase (cyanide and azide) markedly stimulated oxygen uptake of slices for preclimacteric (PC) fruit and caused a slight increase also in slices from climacteric (C) tissue. Amytal which prevents the reduction of cytochrome b also brought about a stimulation in slices of PC and C tissue. However, the stimulation was abolished by the simultaneous use of both amytal and azide. Dinitrophenol (DNP) which enhanced markedly O2 uptake by PC slices had little effect in the presence of amytal and azide. Incorporation of P32 was depressed by the uncoupler and by the combination of inhibitors but not when amytal and azide were used singly. The coexistence of inter-linked phosphorylative and non-phosphorylative pathways of electron transfer is suggested. The stimulations of respiration were ascribed to the increased supply of a limiting cofactor to the phosphorylating sites due to the reduction of the number of active sites by cytochrome chain inhibitors.