Effects of glycerol on the in vitro stability and regulatory activation/inactivation of pyruvate, orthophosphate dikinase of Zea mays L.

Glycerol stabilizes the activity of pyruvate, orthophosphate dikinase extracted from darkened or illuminated maize leaves. It serves as a better protectant of activity than dithiothreitol for the active day-form and the glycerol concentration needed for full protection is inversely related to the level of protein. The night-form of the enzyme is also protected by glycerol not only against inactivation, but also against partial reactivation in storage. Glycerol does not prevent the Pi-dependent activation nor the ADP-dependent inactivation of pyruvate, orthophosphate dikinase, but the rates of both processes are substantially decreased. The ability of the inactive night-form for Pi-dependent activation is also sustained by glycerol for at least 2 h at 20°C, apparently through stabilization of the labile regulatory protein.