In his early work on Citric Acid Cycle, Hans Krebs made measurements of the oxygen consumption by suspensions of muscle cells. He found that addition of fumarate, succinate or malate to cell suspension stimulated oxygen consumption, and that the amount of oxygen consumed was about 10-fold more than amount required for the complete oxidation of added compound. Moreover, the succinate, malate or fumarate wasn’t consumed by cell suspension but was still detectable at the end of the experiment. What is the correct interpretation of such observations?