Question

Which of the following reactions in plants is/are catalyzed by the malic enzymes?

• A. Malate + NADsuperscript{+} → Pyruvate + COsubscript{2} + NADH
• B. Malate + NADsuperscript{+} → Oxaloacetate + NADH
• C. Malate → Fumarate
• D. Malate + NADPsuperscript{+} → Pyruvate + COsubscript{2} + NADPH

Hint:

Malic enzymes catalyze the conversion of malate to pyruvate, generating NADH or NADPH, depending on whether the enzyme is NADsuperscript{+} or NADPsuperscript{+}-dependent.

Answer 1

The Correct Option is A, D

The malic enzymes are involved in the oxidative decarboxylation of malate in plant cells. Let's analyze each option: 
- (A): The reaction Malate + NADsuperscript{+} → Pyruvate + COsubscript{2} + NADH is catalyzed by malic enzyme, which is involved in the conversion of malate to pyruvate, producing NADH and COsubscript{2}. This reaction is a typical reaction catalyzed by the malic enzyme, making \( A \) correct. 
- (B): The reaction Malate + NADsuperscript{+} → Oxaloacetate + NADH represents a malate dehydrogenase reaction rather than a malic enzyme reaction. This is involved in the conversion of malate to oxaloacetate, but it is not catalyzed by malic enzymes. Hence, \( B \) is incorrect. 
- (C): The reaction Malate → Fumarate is catalyzed by malate dehydrogenase or other enzymes, not malic enzymes. This reaction is part of the citric acid cycle but does not involve malic enzymes. Hence, \( C \) is incorrect. 
- (D): The reaction Malate + NADPsuperscript{+} → Pyruvate + COsubscript{2} + NADPH is another example of a reaction catalyzed by malic enzyme, but in this case, NADPsuperscript{+} is reduced to NADPH, which is characteristic of the NADP-dependent form of malic enzyme. Hence, \( D \) is correct. 
Thus, the correct answers are (A) and (D).