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Tyrosinase activity in the larva of the fleshfly, Sarcophaga barbarta

1975; Elsevier BV; Volume: 21; Issue: 7 Linguagem: Inglês

10.1016/0022-1910(75)90263-2

1879-1611

Lynden Hughes, G.M. Price,

Viral Infectious Diseases and Gene Expression in Insects

Abstract When plasma from third instar larvae of the fleshfly, Sarcophaga barbarta , was diluted tenfold with distilled water, lipoproteins precipitated out. After centrifuging, the water supernatant was rendered 30, 50, and 65% to ammonium sulphate, and it was found that the 50% fraction contained 95% of the tyrosinase activity in all the fractions, the enzyme being present in its inactive form or proenzyme. The proenzyme was activated by mixing it with activator isolated from the larval cuticle. After addition of activator there followed a lag period before the rapid phase of activation, the duration of the lag being dependent upon the concentration of both proenzyme and activator. The final activity attained was dependent upon the concentration of proenzyme but was independent of the activator concentration. The level of proenzyme in the plasma rose steadily throughout the third larval instar reaching a maximum in 7 day larvae, formation of the puparium commencing about 24 hr later, the rounded-off white stage (r.o.). At the r.o. and golden-brown stage (1 hr later) the level was still maximal, but 12 hr later at the dark-brown puparial stage no proenzyme was isolatable from the plasma, all the enzyme at this stage behaving as active enzyme. The vast majority (95%) of the proenzyme isolated from plasma in the larval stages and at the r.o. white stage was present in the 50% ammonium sulphate fraction, whereas 1 hr later at the golden-brown stage only 33% of the proenzyme was found in the 50% fraction, 62% now being found in the 65% fraction. At the dark-brown puparial stage 12 hr later, not only was there a further redistribution, but all the enzyme behaved as active enzyme. It is suggested that these changes in the distribution and behaviour of the proenzyme indicate that, in vivo , activation of the enzyme in the blood has taken place over the period r.o. white to the golden-brown to dark-brown puparial stage.