Changes of protein tyrosine phosphorylation in third instar larval integument of the Mediterranean fruit fly, Ceratitis capitata.

Developmental analysis of the tyrosine protein phosphorylation levels in larval integument and partial characterization of the endogenous protein tyrosine kinase activity (PTK) in Ceratitis capitata are described in this study. Larval integument contains high levels of PTK activity at the early stages of the third instar, which progressively declines to low levels in the white pupal stage. An integumental 90-kDa polypeptide was identified to have prominent endogenous PTK activity and follow a similar developmental pattern. The major integumental phosphotyrosine-containing polypeptides have apparent molecular weights of 30, 41, 44, 46, and 54 kDa, respectively. Polypeptides with molecular weights of 62 and 73 kDa were identified as Ser/Thr-containing phosphoproteins and were shown to exhibit high levels of phosphorylation at the middle stage of larval development. These differences are likely to be due to the higher activation state of the protein tyrosine kinase(s) at the early stages of larval development.