Question

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

Answer 1

We know that the TCS cycle / citric acid cycle is a circular process in which there are compounds that are oxidized and recycled, which leads to a permanent consumption of oxygen. We know that compounds such as fumarsto, malsto and succinate contain four carbons and are transformed into oxaloscetate that is composed of four carbons. The cycle returns and begins when acetyl CoA is added and produces citrate that contains 6 carbons. Once again the oxidation of citrate occurs converting into fumarate, malate and succinate, oxidizing up to compounds of four carbons, however when they are completely oxidized, it is not recycled and oxygen consumption decreases, so if there is 10 times less oxygen consumption it will be produced 10 times more in the cyclic case

In the second case, it is observed that when the compounds are recycled, even when oxidation occurs, they reappear in the cycle, which means that they can be detected even if the cell suspension does not consume them.