PHOSPHORYLATION COUPLED WITH THE OXIDATION OF α-KETOGLUTARIC ACID

Abstract

Present evidence indicates that the energy released by cellular oxidations is in part captured in the form of high energy phosphate bonds, and that such phosphorylations represent the major, if not the only, way in which oxidative energy is made available for the performance of the various functions of the cell.Thus it is of the greatest interest to determine the number of high energy phosphate bonds which can be created by the oxidation of each of the various foodstuffs and metabolites.The question of the number of energy-rich phosphate bonds which could be generated by the single step oxidation of ar-ketoglutarate to succinate and the passage of the electrons over the electron transport systems to oxygen was investigated several years ago by Ochoa (l), who concluded that the number was probably 3.0.This figure was consistent with the value of 3.0 earlier estimated to be the ratio of phosphorylations to atoms of oxygen consumed in the complete oxidation of pyruvate to carbon dioxide and water.These values have been widely accepted and used in profitable speculation about the phosphorylations coupled with oxidations in the tricarboxylic acid cycle.Although values as high as those of Ochoa have been seriously questioned by Ogston and Smithies (2), more recently Loomis and Lipmann (3) and Cross et al. ( 4) have published data which suggest that Ochoa's figure is in the correct range.The present paper presents further data obtained with the washed liver particles used in earlier studies.The final experimental conditions were such as to reduce greatly the side reactions which would otherwise result in loss of a considerable fraction of esterified phosphate.In Ochoa's investigation the directly observed P:O ratios averaged less than 2.0 with heart muscle suspensions, whereas conditions have now been found under which it is possible to get directly determined P:O ratios of 3.4 to 3.5 with washed liver particles.This suggests that the true value in cellular metabolism may be 4.0.