Studies on heart phosphofructokinase: The effect of pyridoxal 5′-phosphate on enzyme activity and dissociation

Abstract

Reaction of pyridoxal 5′-phosphate with ε-amino groups of lysine residues in sheep heart phosphofructokinase causes a loss in the catalytic activity of the enzyme. Inactivation is slowed by the presence of Fru-6- P. Maximum inactivation occurs when 4 moles of pyridoxal 5′-phosphate are bound per 100 000 g of enzyme. Reaction with pyridoxal 5′-phosphate in the absence of Fru-6- P causes the enzyme to dissociate at 0°. Warming the dissociated enzyme to room temperature causes it to reassociate. Enzyme with a small amount of bound pyridoxal 5′-phosphate (<1 mole per 100 000 g) is more sensitive to allosteric inhibition by ATP than native enzyme. This is associated with a shift in the acidic portion of the pH-activity curve of the enzyme to higher pH's.