Kinetic Properties of Phosphorylase and 6-Phosphofructokinase of Kalanchoe daigremontiana and Atriplex spongiosa

Abstract

The kinetic properties of phosphorylase (EC 2.4.1.1) and 6-phosphofructokinase (EC 2.7.1.11) extracted from a crassulacean acid metabolism (CAM) plant, Kalanchoe daigremontiana Hamet et Perrier, and a C₄ plant, Atriplex spongiosa F. Muell., were compared. The phosphorylase from the CAM plant was strongly inhibited by P₁ (1 mM), phosphoenolpyruvate (PEP) (2 mM) and glucose (4 mM). The C₄ phosphorylase was less strongly inhibited by P₁, and not at all by PEP or glucose. The C₄ 6-phosphofructokinase was, at K_m levels of substrate, about 100 times more sensitive to inhibition by PEP than the CAM enzyme. These results are discussed as the basis for a biochemical regulation of carbohydrate metabolism in CAM plants at night.