Double effect of organic amines (activation and inhibition) on the phosphotriesterase

The kinetic behavior of the phosphotriesterase in the presence of organic amines (diethylamine, diisopropylamine, triethylamine, pyridine and others) capable of activating the enzyme at the concentration up to 0.10 M and inhibiting it at higher concentrations is described. The form acting as activator in a solution is the nonprotonated form of amines and the value of activation effect depends on pKa of amine and its structure. The activation by amines at the above concentrations has a noncompetitive character, whereas the inhibition at higher concentrations has competitive one. The mechanism of phosphotriesterase action in the presence of amines is discussed.