A student listed the following combinations of enzymes and their involvement in different phases of the Calvin-Benson cycle:
A. Phosphoglycerate kinase – Reduction phase
B. Glyceraldehyde-3-phosphate dehydrogenase – Regeneration phase
C. Triose-phosphate isomerase – Reduction phase
D. Phosphoribulokinase – Regeneration phase

Which one of the following combinations is correct?

Correct option is D

Explanation-

A. Phosphoglycerate kinase – Reduction phase - CORRECT
This enzyme is involved in converting 1,3-bisphosphoglycerate to 3-phosphoglycerate using ATP → part of the reduction phase.
B. Glyceraldehyde-3-phosphate dehydrogenase – Regeneration phase - INCORRECT
Actually functions in the reduction phase, not regeneration.
C. Triose-phosphate isomerase – Reduction phase - INCORRECT
Although it acts on products of the reduction phase, its main role is in rearranging carbon skeletons, which is important for regeneration, not reduction.
D. Phosphoribulokinase – Regeneration phase - CORRECT
Key enzyme in the regeneration phase, helps regenerate RuBP.

Correct combination is: A and D only
Thus, the correct answer is: Option d – A and D only.