The effect of heat hardening on the heat resistance of some enzymes from plant leaves.

Heat hardening of leaves which leads to an increase in the heat resistance of their cells, also increases the heat resistance of their enzymes (urease, acid phosphatase, ATPase). As judged by the temperature reducing enzyme activity by 50%, the heat resistance increased by about 6° and 4°, respectively, for urease and acid phosphatase of cucumber, about 7° for acid phosphatase of wheat, and 1,5° for ATPase of Caragana. Increased heat resistance of acid phosphatase and ATPase caused by heat hardening was accompanied by a decrease in the activity ofthese enzymes. The activity of urease was not affected by heat hardening. It is assumed that the cause of this increase in thermal resistance of enzymes is a stabilization of protein macromolecules during heat hardening of leaves.