Human Pb, human post-Pb, and nonhuman primate Pb proteins: immunological and biochemical relationships.

The isolation and characterization of a protein from human parotid saliva termed the "post-Pb protein" is described. By several criteria, this protein is closely related to the human Pb proteins. When reacted against antisera to human Pb protein in double diffusion, the post-Pb protein is found to be related to the Pb proteins by lines of identity. However, when the partial N-terminal amino acid sequences of the post-Pb protein and Pb proteins are compare, the sequences are not identical. Because of the similarity in size of the Pb and post-Pb proteins and because of the observed sequence differences, any product-precursor relationship between the Pb and post-Pb proteins is unlikely. The post-Pb protein probably is the product of a genetic locus different from the Pb locus. Two additional species of nonhuman primates (Papio papio and P. sphinx) have been found to have Pb proteins electrophoretically similar to these found in the rhesus monkey and differing from those in the human. The isolated Pb proteins of the rhesus monkey have been found to have close biochemical and immunological relationships to the human Pb proteins.