The isolation and characterization of proteins from the left colleterial gland of the cockroach, <i>Periplaneta americana</i> (L.)

Abstract

Abstract Previous work has established that the cockroach egg-case is constructed of proteins which are cross-linked by reaction with the oxidation products of ortho-diphenols. In the present study the predominant proteins of the egg-case were isolated, before they had been crosslinked, from the secretion of the left colleterial gland. They can be separated into waterinsoluble proteins in the form of globules which can be seen in the electron microscope, and water-soluble proteins. When these two fractions were separated from each other by sucrose density gradient centrifugation, phenol oxidase activity was found to be associated with the water-soluble proteins. Electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulphate shows that the water-insoluble protein fraction contains two major and one minor proteins; the water-soluble protein fraction contains three major proteins. The molecular weights of these proteins were determined from their mobilities on electrophoresis by this method. The proteins were separated by gel filtration chromatography and the homogeneity of the individual fractions was tested by electrophoresis and iso-electric focusing on polyacrylamide gels. The amino acid composition of each protein fraction was obtained. The two major water-insoluble proteins have high contents of glycine, tyrosine and leucine, and two of the water-soluble proteins have high contents of glycine, tyrosine and valine. The minor protein of the water-msoluble fraction and the third wrater-soluble protein have identical electrophoretic mobilities and relatively high contents of Lysine, proline and valine. The compositions of the four proteins with high contents of glycine show some resemblances to those of silks but are significantly different from anything previously described. The high tyrosine contents of these four proteins suggest that tyrosyl residues may be involved in the formation of the cross-links.