Larval cuticle proteins of Lucilia cuprina: Electrophoretic separation,quantification and developmental changes

Proteins from isolated cuticles of third instar larvae of the sheep blowfly, Lucilia cuprina, have been solubilized with water or 7 M urea or 2% SDS. While 7 M urea or 2% SDS extract significantly more protein than water, the same major proteins, in the same relative proportions, are extracted by all three solutions. More than 80% of the cuticular protein is extracted by 7 M urea or 2% SDS. Extracted proteins resolve into nine major bands when analysed by gradient polyacrylamide gel electrophoresis. These proteins are anionic, relatively low in molecular weight (13–28 kd) and are essentially free of carbohydrate. Only minor differences exist between the proteins of two morphologically distinct cuticular regions. Cuticle proteins, extracted from larvae at different developmental stages (first, second and third instars) display quantitatively and qualitatively unique electrophoretic profiles. A number of proteins are common to all stages however. The electrophoretic profiles of proteins extracted from larval cuticles at various times within an instar also differ although the differences are largely quantitative. This is particularly evident during the transition from the feeding to the wandering stages of the third instar; the weight of the cuticle relative to that of the larva increases and this is accompanied by marked changes in the electrophoretic profile of the cuticle proteins.