Jc. Servaites et Dr. Geiger, REGULATION OF RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE BY METABOLITES, Journal of Experimental Botany, 46, 1995, pp. 1277-1283
Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and other en
zymes and their common metabolites form a system regulated by feedforw
ard and feedback mechanisms that is directly involved in assimilation
of carbon, The interaction of these components in the chloroplast give
s rise to properties, which can not be predicted from the study of iso
lated components alone, Experiments were conducted to explain how the
observed pattern of system level regulation is consistent with the ind
ividual characteristics of Rubisco measured in vitro, In vitro Rubisco
is responsive to a wide range of ribulose 1,5-bisphosphate and phosph
oglycerate concentrations, similar to those found in leaves under fiel
d conditions, Metabolite regulation of carbon assimilation in vivo inv
olves several processes. Among these are negative co-operativity of ri
bulose 1,5-bisphosphate binding by Rubisco, competitive inhibition of
Rubisco by phosphoglycerate and inorganic phosphate, a high Rubisco ac
tive site concentration in the chloroplast, and maintenance of a const
ant phosphate concentration in the chloroplast resulting in reciprocal
changes in the concentrations of ribulose 1,5-bisphosphate, phosphogl
ycerate and inorganic phosphate, High-light-grown plants exhibited hig
her assimilation rates than those growing under moderate light levels,
but had similar Rubisco concentrations, Larger ribulose 1,5-bisphosph
ate/phosphoglycerate ratios in plants grown outdoors are responsible f
or the higher Rubisco activities and greater rates of carbon fixation
observed under these conditions.