Effects of temperature on the activity of phosphoenolpyruvate carboxylase and on the control of CO2 fixation in Bryophyllum fedtschenkoi
1995
Carter, P.J. | Wilkins, W.B. | Nimmo, H.G. | Fewson, C.A.
The phosphorylation state and the malate sensitivity of phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31) in Bryophyllum fedtschenkoi Hamet et Perrier are altered by changes in the ambient temperature. These effects, in turn alter the in-vivo activity of the enzyme. Low temperature (3 degrees C or less), stabilizes the phosphorylated form of the enzyme, while high temperature (30 degrees C) promotes its dephosphorylation. The catalytic activity of the phosphorylated and dephosphorylated forms of PEPCase increases with temperature, but the apparent Ki values for malate of both forms of the enzyme decrease. Results of experiments with detached leaves maintained in darkness in normal air indicate that the changes in malate sensitivity and phosphorylation state of PEPCase with temperature are of physiological significance. When the phosphorylated form of PEPCase is stabilized by reducing the temperature of leaves 9 h after transfer to constant darkness at 15 degrees C, a prolonged period of CO2 fixation follows. When leaves are maintained in constant darkness at 15 degrees C until CO2 output reaches a low steady-state level and the PEPCase is dephosphorylated, reducing the temperature to 3 degrees C results in a further period of CO2 fixation even though the phosphorylation state of PEPCase does not change.
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