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Plant and Cell Physiology, 1974, Vol. 15, No. 2 373-379
© 1974

Article

Kinetics of cold inactivation and heat reactivation of the ribulose diphosphate carboxylase activity of crystalline Fraction I proteins isolated from different species and hybrids of Nicotiana

Shalini Singh and S. G. Wildman

Department of Biology, Molecular Biology Institute, University of California Los Angeles 90024, U.S.A.

The maximum specific ribulose diphosphate carboxylase activity of crystalline Fraction I proteins isolated from 8 species, and 12 reciprocal, interspecific, F1 hybrids of Nicotiana changed to minimum specific activity between 16 and 20 hr after the enzymes at 25°C were placed in ice baths. The minimum state was preserved for more than one year without further change when crystals of enzymes were suspended in buffer at 0°C. At any time during cold storage, the maximum state of specific activity could be regained by dissolving the crystals in buffer containing NaCl and heating the solution at temperatures up to 50°C. Maximum activity was attained by heating at 50°C for 20 min whereas more than 100 hr was required at 25°C.

An equilibrium was demonstrated between maximally active and minimally active enzyme molecules. The equilibrium constant was a function of the storage temperatures between 0° and 25°C. The molar enthalpy, {Delta}H, separating maximally active from minimally active enzyme molecules was 3.75±0.1 kcal/mole, an energy difference consistent with previous findings that the change in specific activity did not result from dissociation of subunits or depolymerization of aggregates.

The effect of cold storage of Nicotiana enzyme would seem to offer a molecular basis for explaining the effect of cold temperatures on photosynthetic CO2 fixation by winter wheat leaves which was shown by Sawada and Miyachi (5) to produce an accumulation of ribulose 1–5 diphosphate and diversion of the normal path of photosynthetic CO2 fixation away from phosphoglyceric acid to the appearance of fixed carbon in serine and glycine by the glycolate path.

(Received October 22, 1973; )
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