Effects of guanidine inhibitors on mung bean mitochondria

The effects of phenylethylbiguanidide, decamethylenediguanidide, and octylguanidine have been studied with mung bean hypocotyl mitochondria (Phaseolus aureus var. Jumbo) supplied with malate, reduced nicotinamide adenine dinucleotide, succinate, or ascorbate-tetramethyl-p-phenylenediamine as substrates. The guanidines act as energy transfer inhibitors, all three inhibiting all three phosphorylation sites. Phenylethylbiguanidide causes only partial inhibition even at relatively high concentrations. Decamethylenediguanidide inhibits about 70% of the malate respiration, 55% of the succinate respiration, and 35% of the ascorbate-tetramethyl-p-phenylenediamine respiration.Octylguanidine inhibits all three phosphorylation sites and the cyanide-insensitive respiration, but to differing extents and at different concentrations. Both states 3 and 4 are inhibited by octylguanidine. Inhibition of state 4 is preceded by an uncoupling action at lower concentrations of inhibitor, while inhibition of state 3 is influenced by the state of the mitochondria when the inhibitor is added. Application of the guanidine to state 4 mitochondria is more effective than application to mitochondria already in state 3.