Abstract
The ability of glutamate + malate, 2-oxoglutarate, NADH, succinate and DL-lactate to support oxidative phosphorylation, the formation of membrane potential, swelling and Ca 2+ uptake in Euglena mitochondria was studied. Oxidative phosphorylation was supported by the five substrates assayed with the appropiate ADP/O ratios ad high respiratory control values. Oxidative phosphorylation supported by lactate was resistant to antimycin, but sensitive to 2-heptyl-4-hydroxyquinoline- N-oxide (HQNO), myxothiazol and cyanide. Respiration and membrane potential resistant to cyanide were observed with lactate and, to a lesser extent, with glutamate + malate. A similar pattern of inhibition, confirmed in thisstudy, has been described for oxidation of D-lactate in bacterial systems. Oxidation of lactate induced an increase in matrix NAD(P)H; however the retention of lactate oxidase activity in submitochondrial particles suggested that, similar to lactate oxidation in bacterial systems, NAD(P) was not an essential requirement in this reaction. Substrate oxidation induced swelling whereas ATP synthesis caused shrinkage. Ca 2+ uptake was only partially inhibited by ruthenium red and was completely abolished by an uncoupler.
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