SUBSTRATE SPECIFICITY AND DEVELOPMENTAL CHANGES OF ACETYLCHOLINESTERASE IN COTTON BOLLWORM*

Abstract

Abstract The substrate specificity and developmental changes of acetylcholinesterase (AChE) of cotton bollworm, Helicoverpa armigera Hübner, were investigated during 1991 to 1994. The insects were collected from Handan suburbs of Hebei Province and Guan County of Shandong Province. The results show that the specific activity and Michaelis constants (km) of AChE toward acetylthiocholine (ATCH) and acetyl‐β‐methyl‐thiocholine (MeTCh) regularly varied with the developmental stage of cotton bollworm. The two peaks of the specific activity were observed respectively in the third instar and sixth instar of larvae. The specific activity of AChE in pupae was the lowest and that in heads of four‐days moth was the highest in various developmental stages of cotton bollworms. The tendency of Km and maximum velocity (Vmax) was identical with the change of specific activity in the AChEs of cotton bollworm. The activation energy (Ea) of AChE toward MeTCh in pupae and adults was 3. 9–4. 3 times as much as that of, larvae in cotton bollworms from Handan of Hebei Province. It suggests that the spending energies of AChE for hydrolysing substrate are different in larva, pupa and adult. The optimum conditions of AChE reaction with ATCh in larvae were 50–100 mg of tissue weights for the amount of enzyme, 10–20 minutes for the reaction time, 35°C for the reaction temperature and 8. 0 for the reaction pH value.