HYDROLASE ACTIVITY IN PLODIA-INTERPUNCTELLA - USE OF DIFLUBENZURON AND P-NITROACETANILIDE AS SUBSTRATES

The optimal conditions for diflubenzuron hydrolase activity in Plodia interpunctella were determined using [C-14]diflubenzuron (I)FB) as sub strate. The radiolabeled metabolites 4-chloroaniline (4-CA) and 4-chlo rophenylurea (4-CPU) were separated and quantitatively evaluated. Prof enofos and S,S,S-tributyl phosphorotrithioate inhibited the enzyme act ivity in vitro, profenofos being more active. Hydrolysis was also inhi bited in the presence of p-nitroacetanilide (pNAA), resulting in a 66% decrease in the release of 4-CA; the release of I-CPU was not affecte d. pNAA hydrolase activity was higher in the prepupa than in the larva l stages. Profenofos inhibited pNAA hydrolase activity to a much great er extent than DEF. The enzyme activity was inhibited by DFB at relati vely high concentrations. Determination of Michaelis-Menten kinetics w ith and without DFB revealed typical competitive reversible inhibition plots. The inhibition depended on the concentrations of enzyme, subst rate, and inhibitor. Inhibition of pNAA hydrolysis occurred in the pre sence of DFB or its antibodies. Our findings indicate the possibility of using pNAA as a surrogate substrate for DFB hydrolase activity. The enzyme assay is accurate and easy to perform and may open up new aven ues of research aimed at evaluating defense systems and resistance mec hanisms to DFB and other benzoylphenyl ureas. (C) 1995 Academic Press. Inc.