question_answer 64)

  Why is the RuBisCo enzyme more appropriately called RUBP carboxylase-oxygenase and what important role does it play in photosynthesis?

Answer:

                  RuBP carboxylase and oxygenase has dual nature. It has affinity for both  and  but has more affinity for  than . Thus, the concentrations of two determines which of the two will bind to the enzyme. Consider the following two situations (i) In a normal condition when  and  concentrations are normal, it acts as carboxylase and fix  ,by combining with ribulose bisphosphate and  cycle operates normally, producing glucose molecule as an first product of photosynthesis. (ii) If  concentration goes up and  goes down, it starts acting as an oxygenase enzyme and Cg cyole (photorespiration) starts where RuBP binds with  to from phosphoglycolate. (iii)  plants have mechanisms to increase the concentration of at enzyme site, and increasing the intracellular concentration of . Thus, here RuB is Co acts as carboxylase, minimising the affect of oxygenase.