Isolation and characterization of three major larval serum proteins of the mediterranean fruit fly Ceratitis capitata (Diptera)

Three major larval serum proteins (MLSP-1,2 and 3) of the Dipteran species Ceratitis capitata have been isolated and characterized. The structure of these proteins was found to depend on the pH. At acidic pH, they form hexamers which dissociate above pH 6.5. Their dissociation pattern in the pH range 6.5–8.5 was studied by gel filtration analysis. MLSP-3 was found to be the most readily dissociated protein followed by MLSP-1 and 2. Our data suggest that, in vivo, these proteins associate randomly to both homo- and heterohexameric forms. Amino acid analysis and partial peptide mapping, indicated the high degree of homology in the primary structure of these proteins, especially between MLSP-1 and 2. Partial homology of these three proteins with MLSP-4, another major larval serum protein of C. capitata which has been isolated previously in our laboratory (Mintzas and Rebutsicas, 1984) was also found. The amino acid analysis suggested the presence of glucosamine in MLSP-1, 2 and 3 while neutral sugars were identified only in MLSP-1 and MLSP-4.