Isolation and characterization of BCP 54, the major soluble protein of bovine cornea

Abstract

The most abundant soluble protein of bovine cornea, which we have named “BCP 54” (Bovine Corneal Protein, molecular weight 54000 daltons), has been isolated and biochemically characterized. This protein constitutes approximately 30% of the total soluble protein of whole cornea. BCP 54 is present in both epithelium and stroma; however, its presence in endothelium has not been demonstrated conclusively. Immunochemical analysis indicates that BCP 54 is of corneal, but not of serum, origin. Polyacrylamide gel electrophoresis in SDS of either unreduced or reduced BCP 54 yields a single protein band with a molecular weight of 54000 daltons. By gel filtration the molecular weight of the native molecule was also shown to be about 54000 daltons. Isoelectric focusing under denaturing conditions yields four bands clustered between pH 6·6 and pH 6·9. Thus BCP 54 appears to be a protein composed of a single polypeptide chain, but with some degree of microheterogeneity. The amino acid composition of BCP 54 demonstrates that it is not a collagenous or actin-like protein; furthermore, it is not a glycoprotein. The abundance and distribution of BCP 54 suggest that this protein fulfills an important, but as yet unknown, function in the cornea.