Abstract
Variations in the method of preparing heart-muscle sarcosomes had little effect on yield of oxidative phosphorylation (P:O ratio) coupled with oxidation of alpha-ketoglutarate to succinate, although the QO2 of the alpha-ketoglutaric oxidase system was considerably affected. The P:O ratio was little changed if the sarcosomes were mixed with other muscle components. For accurate measurement of the P:O ratio, it is necessary to purify the yeast hexokinase prepn. so that it no longer catalyzes an anaerobic reaction of alpha-ketoglutarate. The further oxidation of succinate is not stopped completely by addition of 0.01 [image] malonate and 0.04 [image] fluoride. Under these conditions, an avg. of 1.13 atoms of 02 were consumed per mole of alpha-keotglutarate disappearing. The concn. of all components of the reaction mixture can be varied considerably without affecting P:O ratio. Measurements of the P:O ratio on 32 sarcosomal prepns. are presented and analyzed. In contrast to measurements in other laboratories, but in agreement with Ochoa''s (1944) original assessment, the P:O ratio for the oxidation of alpha-ketoglutarate to succinate is concluded to be 3. The high values obtained by other workers are probably due to underestimation of the 02 uptake, and on one case to over-estimation of rate of phosphorylation.