Isolation and partial characterization of human parotid basic proteins.

Methods are presented for the isolation of basic proteins (Pb proteins) from human parotid saliva collected from humans possessing different alleles at the Pb locus. The proteins were found to be extremely basic, with an isoelectric point above 9.5. They contain approximately 45% of the basic amino acids histidine, lysine, and arginine, and are devoid of cysteine, proline, threonine, valine, methionine, and tryptophan. They are free of carbohydrate. A comparison of the amino acid sequence data of Pb protein to all available amino acid sequences revealed that no sequence similarities exist between the Pb proteins and any other proteins reported, although proteins of similar amino acid compositions have been reported by others. A model is presented with accounts for the several forms of allelic proteins based on observed amino acid sequence differences.