Photosynthesis Question 77
77. The enzyme which fixes $CO_2$ in $C_4$ plants is
(a) Hydrogenase
(b) PEP carboxylase
(c) Reductase
(d) RuBP carboxylase
Show Answer
Answer : b
Hints & Solution
(b) The three most important roles that PEP carboxylase plays in plants and bacteria metabolism are in the $C_4$ cycle, the CAM cycle and the Citric Acid Cycle biosynthesis flux. PEP carboxylase plays the key role of binding $CO_2$ to create oxaloacetate in the mesophyll tissue. $C_4$ plants have carboxylating enzymes that have a higher affinity for $CO_2$, compared to rubisco, especially at low $CO_2$ concentrations & high temperatures. The $C_4$ pathway uses PEP carboxylase, which has a much higher affinity for $CO_2$ than rubisco; in addition, PEP carboxylase does NOT have oxygenase activity.
