Serum albumin and its acid hydrolysis peptides dominate preparations of mineral-bound enamel proteins.

Serum albumin is a major noncollagenous protein component of bone, dentine, and, according to our results, enamel. Preparations of mineral-bound proteins from porcine developing enamel contain a single 67 kD protein at neutral pH or three proteins (67, 63, and 53 kD) at low pH that were assumed to be enamelins, a minor class of enamel proteins. A more complete analysis of these proteins in this study showed that they were derived from porcine serum albumin (PSA). This was demonstrated by amino acid analysis, by N-terminal sequence analysis, by immunoblot studies using an anti-PSA antibody, and by SDS-PAGE analysis of the acid hydrolysis, cyanogen bromide, and tryptic peptides. Examination of enamel at different developmental stages showed that PSA deposited in enamel from the enamel organ and from the dentine during development, not during the dissection process. These results indicate that true enamelins must represent a very small fraction of the total mineral-bound protein matrix in porcine developing teeth, and this has important implications on the role of mineral-bound proteins during mineralization of enamel.