Abstract
Thiamine monophosphate pyrophosphorylase (EC 2.5.1.3) has been purified approximately 320-fold from baker's yeast, and the kinetic studies were carried out in the presence of several organic phosphate compounds and metabolites. High-energy phosphate compounds including ATP, ADP acetyl phosphate, phosphoenolpyruvate inhibited the enzyme activity at the physiological concentrations in yeast. The effectors were noncompetitive with respect to both substrates and caused no change in the apparent Km for both substrates with a decrease in V_<max>. A shift of pH optimum to the alkaline side was observed in the presence of the effectors and the enzyme tended to be desensitized to the effectors at pH 9.0,with partly loss of enzyme activity. A metabolic role of these effectors to the enzyme in yeast is discussed.
