A method of measuring the yield of oxidative phosphorylation

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Abstract
The yield of oxidative phosphorylation may be measured by the enzymic detn. of hexosemonophosphate, which is the end product of the reaction when hexokinase and glucose are added. This method has certain advantages over the more commonly employed procedure of measuring the disappearance of inorganic phosphate. A number of side reactions, catalyzed by enzymes present in the heart-muscle sarcosomes or in the hexokinase prepns., were investigated from the point of view of possible interference in the measurement of the phosphorylation. The myokinase reaction which causes formation of hexosemonophosphate in the absence of oxidative phosphorylation can be made very slow by the addition of 2 inhibitors (fluoride and adenylic acid) and may be allowed for in a control. Adenosinetriphosphatase activity of the sarcosomes is considerable, but can be eliminated as a source of error by the addition of sufficient hexokinase. The very slight hexosemonophosphatase and phosphohexokinase activity causes negligible errors. No glycolysis occurs under the conditions of the oxidative phosphorylation expts. It is concluded that the amt. of hexosemonophosphate found is an accurate measure of the yield of oxidative phosphorylation.