Harmaline interactions with yeast invertase

The effect of harmaline, a plant alkaloid has been studied on yeast invertase activity in the absence and presence of 50mM Na+ as a function of pH. Harmaline (1-3 mM) inhibited the invertase activity at pH 5.2, 6.8 and 8 both in the absence (44-92%) and (22-85%) of Na+ ions. Kinetic analysis revealed that harmaline is a non-competitive inhibitor of invertase, at pH 5.2 and 6.8 but at pH 8, it produced a mixed type of inhibition, Km increased by 450% and 175% and Vmax decreased by 82% and 63% in the absence and presence of 50mM Na ions respectively. The observed inhibition of invertase by harmaline was reversible in nature. These findings suggest that the presence of Na+ site is not a prerequisite for the inhibition of enzyme by harmaline.