CHARACTERIZATION OF THE ARYLALKYLAMINE N-ACETYLTRANSFERASE IN ONCHOCERCA-VOLVULUS

The characteristics and kinetic properties of an arylalkylamine N-acet yltransferase were studied in partially purified preparations of the h uman filarial parasite Onchocerca volvulus. The enzyme, which had a re lative molecular mass (M(r)) of 37-38 kDa, catalyzed the acetylation o f arylalkylamines but did not accept arylamines or polyamines as subst rates. The optimal pH for enzyme activity was found to be 8.5 in TRIS- HCl. The apparent Michaelis constant (Km) and maximum velocity (Vmax) determined from Lineweaver-Burk plots for tryptamine were 1.8 mu M and 29 nmol min(-1) mg and protein(-1), respectively. Except for the cate cholamines, the other arylalkylamines such as 5-hydroxytryptamine (5-H T), tyramine, and octopamine similarly exhibited high affinities and r eaction rates. Whereas the enzyme is inhibited by metals and p-chloro- mercuribenzoate, it is inactivated neither by amethopterin nor by cyst amine and is thereby distinguished from the mammalian arylamine N-acet yltransferase. Like other N-acetyltransferases whose function is the r egulation of intracellular amine levels, the enzyme may have a role in the inactivation of excess biogenic amine in this parasite.