Question

You are doing a biochemical experiment and observed that addition of small amounts of oxaloacetate (OAA) or malate to suspensions of minced pigeon muscle tissue incubated in glucose solution quickly increased the observed CO2 production to levels about seven times more than amount of carbon added as OAA. Explain in a brief statement (1-2 sentences) why is the amount of CO2 produced is so much greater than the number of carbons in the added OAA?

Answer 1

Answer: Oxaloacetate or malate is regenerated in the TCA cycle, which produces considerable amount of CO2 in cellular respiration (2 CO2 are produced per acetyl CoA). When OAA or malate is added, they get regenerated again and again, thereby increasing the catalytic rate of acetyl CoA and producing CO2 way beyond the normal OAA CO2 production.

Explanation (for reference): During normal cellular respiration, glycolysis produces pyruvate, which is then broken down to acetyl CoA and CO2. Acetyl CoA is then broken down to 2 CO2 by TCA cycle. Oxaloacetate (OAA) or malate in normal TCA cycle is regenerated and hence, no fresh input of OAA or malate is required by the cell for TCA cycle. However, when OAA or malate is added exogenously to muscle tissue, there will be regeneration of OAA or malate when the molecules are inducted in TCA cycle. Hence, the catalytic rate of TCA cycle increases, with more and more acetyl CoA being broken down to CO2. Hence, the CO2 production will increase 7 times the amount that is released when the TCA cycle is normally operating in the muscle.