Effect of hydroxamic acids from cereals on aphid cholinesterases

Abstract

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid involved in the resistance of wheat to the aphid Rhopalosiphum padi, and known to react with serine and cysteine residues, inactivated acylcholinesterases (acylcholine hydrolases, EC 3.1.1.7) from homogenates of whole bodies of adult R. padi. The enzyme preparation was shown to consist mainly of acetylcholinesterase (AChE) containing an essential cysteine residue outside the substrate binding site. AChE from R. padi, and also ChE from other insects and from human erythrocytes which do not possess such a cysteine residue, were inhibited (I50 in the mM range) by DIMBOA. 4-Hydroxy-7-methoxy-1,4-benzoxazin-3-one, a compound known to react with cysteine residues but not with serine residues, did not inactivate AChE from R. padi under similar conditions. The results suggest that inactivation of AChE from R. padi by DIMBOA does not occur through reaction with its characteristic cysteine residue. © 1993.