Chemical and physical characterization of a phosphoprotein, Protein C, from human saliva and comparison with a related protein A.
The isolation of a highly purified phosphoprotein, previously named protein C, from human parotid saliva is described. A chemical and physical characterization of protein C was undertaken and the properties of protein C were compared with those of a related protein A. The content of glycine, proline and dicarboxylicamino acids accounts for 83% of the total resideus of protein C and it contains 2.0 mol of P/mol of protein, most likely as phosphoserine. The protein also contains 1.2% glucose, but no hexosamine. The N-terminus is blocked and the proposed C-terminal sequence is -Ser(Gly, Pro)Gln. The molecular weight determined from ultracentrifugation is 16300. Circular dichroism and nuclear magnetic resonance fail to demonstrate the presence of polyproline structure, and there are no conformational changes under a variety of conditions. With specific antisera to protein C the protein can be detected in submandibular as well as in parotid saliva, but there is only reaction of partial identity of proteins A and C. It is proposed that at least part of the difference between proteins A and C is due to the presence of an additional length of peptide at the C-terminus of protein C.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D002942:Circular Dichroism; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D010750:Phosphoproteins / Q000032:analysis* / Q000302:isolation & purification; D010758:Phosphorus / Q000032:analysis; D012463:Saliva / Q000032:analysis*
D000596:Amino Acids; D002241:Carbohydrates; D010750:Phosphoproteins; D010758:Phosphorus