The effect of pyridoxal phosphate on the activity of aldolase from Lemna minor L.

Lemna aldolase has been purified by ion-exchange and affinity chromatography. The enzyme is inhibited by pyridoxal phosphate in a manner which suggests that pyridoxal phosphate forms a non-covalent complex with the enzymes which is in equilibrium with the Schiff base covalently modified enzyme. The kinetics of the reversal of inhibition have been used to test the proposition that the fall in aldolase activity observed during periods of nitrogen starvation is due to inhibition by pyridoxal phosphate. It is concluded that the in vivo loss of aldolase activity is not due to pyridoxal phosphate and that the in vitro inhibition of glycolytic enzymes by pyridoxal phosphate is due to the reaction with lysine residues at the active sites which are necessary to bind the strongly acidic sugar phosphates.