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.
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