Metabolism of beta-[3-H]ecdysone during the larval-pupal stage of the blowfly Calliphora erythrocephala.

in aggregation of some of the enzyme. This has previously been suggested to take place in the housefly, Musca vicina (Ohnishi, 1958) and the blowfly, Calliphora (Mum & Bufton, 1973). When gels of the 50 %-satd. fraction were incubated with tyrosine (0.002~) only one band of activity was discernible and this corresponded to the slowest running catecholase band (Fig. le). The result shows that there may be at least two catecholases and one tyrosinase of a molecular size that allows their inclusion in a 5 % polyacrylamide gel. The amount of activator in the cuticle was high throughout the third larval instar, 3-8 day larvae. When a fixed amount of proenzyme was mixed with various amounts of activator there followed a lag period before activation took place, the duration of which was inversely proportional to the activator concentration. However, the maximum activity attained was the same in each case, indicating that activation was due to a factor in the cuticle fraction activating an enzyme in the plasma fraction and not vice versa. Under the conditions of activation described above, neither a-chymotrypsin nor trypsin could replace the cuticle extract. We conclude that if activation of tyrosinase in Sarcophaga involves a partial proteolysis, as has been shown in Bombyx mori (Ashida et al., 1974), then a higher degree of specificity is exhibited by the Sarcophaga cuticle activator.