A STRUCTURAL PROTEIN THAT PLAYS AN ENZYMATIC ROLE IN THE EGGSHELL OF DROSOPHILA-MELANOGASTER

E.S.P. is responsible for the hardering process of the egg-shell at the end of oogenesis (stage 14B) and constitutes a structural component. By immunoblotting, using polyclonal rabbit anti-HRP antibody and anti-rabbit IgG-HRP or Protein A-125I as second antibody, one major band with MW 38KD on nitrocellulose filter showed positive reaction. We conclude that the E.S.P. is identical to the S38 chorionic protein. Morphological immunogold staining, using pre-embedding procedure, revealed positive reaction in the innermost chorionic layer (ICL) and the endochorion of the eggshell. In addition, electron probe X-ray microanalysis revealed the existence of 37% calcium (explained since the enzyme is Ca2+ -activated) and 5% iron (explained due to the fact that it is a haemoprotein). © 1991.