Oxaloacetate is formed from malate in the citrate cycle and can then enter another round of the cycle or be used to form other molecules. However, heme cofactors cannot be derived from oxaloacetate, unlike phosphoenolpyruvate, citrate, and aspartate, which are potential fates for oxaloacetate through enzymatic conversions like those catalyzed by aspartate transaminase, citrate synthase, and phosphoenolpyruvate carboxykinase.

1. In the citrate cycle, oxaloacetate is formed from malate. Oxaloacetate is then used as the starting
substrate in another round of the citrate cycle. But oxaloacetate is also a precursor for many other
molecules. Which of the following is NOT a potential fate of the molecule oxaloacetate? Choose
one: O A. heme cofactors O B. phosphoenolpyruvate O C. citrate O D. aspartate
Solution
Ans 1 : A) heme cofactors
Heme cofactors cannot be formed out of oxaloacetate , whereas the rest all other molecules such
as aspartate , citrate and phosphoenolpyruvate can be synthesised by oxaloacetate.
Different enzymes such as aspartate transaminase , citrate synthase and phosphoenolpyruvate
carboxykinase catalyse these conversions.