title: Structural proteins in the egg-shell of the oriental garden cricket, Gryllus mitratus.
abstract: 1. The egg-shell of the oriental garden cricket, Gryllus mitratus, contained at least two different types of structural protein in an approximate ratio of 5:1. The major fraction was extracted in a solvent containing dithiothreitol, EDTA and 8m-urea, and was purified to apparent homogeneity as judged by free-boundary electrophoresis and ultracentrifugation. This was designated SH-fraction and its S-carboxymethyl derivative (CM-fraction) was also prepared. The minor fraction, insoluble in the solvent, was designated insoluble residue. 2. The major fraction was a phosphoprotein, rich in serine (29.8mol% of the total amino acids) and phosphate (nearly equimolar to serine), and O-phosphoserine was identified in its partial acid hydrolysate. The content of cystine was rather low (0.9mol%) in spite of the importance of this amino acid residue in the native form of the protein. The insoluble residue contained only a small amount of phosphorus, and its amino acid composition was clearly different from the major fraction. 3. CM-fraction, a fibrous protein with an average molecular weight of 57500, behaved as a typical polyanion owing to the high content of phosphate. SH-fraction and CM-fraction were precipitable from their aqueous solutions by the addition of bivalent metal cations, and the precipitation of CM-fraction by Ca(2+) and Mg(2+) was studied in detail. 4. When SH-fraction was exposed to air, intermolecular disulphide linkages were formed, yielding a net-like gel that changed its volume with changes in Ca(2+), Mg(2+) and Na(+). 5. The possible role of this protein fraction in maintaining the integrity of the egg-shell, and a comparison of its composition and properties with other egg-shell proteins and other phosphoproteins, are discussed.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002118:Calcium; D011232:Chemical Precipitation; D003553:Cystine / Q000032:analysis; D004220:Disulfides; D004229:Dithiothreitol; D004492:Edetic Acid; D004586:Electrophoresis; D005260:Female; D005782:Gels; D007313:Insecta / Q000032:analysis*; D008274:Magnesium; D008970:Molecular Weight; D010063:Ovum / Q000032:analysis*; D010710:Phosphates / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis; D011506:Proteins / Q000032:analysis*; D012694:Serine / Q000032:analysis; D012964:Sodium; D014461:Ultracentrifugation; D014508:Urea
chemical_list: D000596:Amino Acids; D004220:Disulfides; D005782:Gels; D010710:Phosphates; D010750:Phosphoproteins; D011506:Proteins; D012694:Serine; D003553:Cystine; D014508:Urea; D004492:Edetic Acid; D012964:Sodium; D008274:Magnesium; D002118:Calcium; D004229:Dithiothreitol