A phosphorylated keratohyalin-derived precursor of epidermal stratum corneum basic protein.

The precursor of the cationic protein called stratum corneum basic protein (SCBP) has been purified from extracts of epidermal keratohyalin granules. The precursor and SCBP have virtually identical amino acid compositions and similar reactivities to antibody to SCBP. Peptide mapping studies using elastase in sodium dodecyl sulfate (SDS)-polyacrylamide gels suggest that the primary amino acid sequences of SCBP and the precursor are similar. The proteins differ in their mobilities on SDS-polyacrylamide gel electrophoresis and in their net charges. The lower pI of the precursor (6.9) appears to be due to 15 to 20 mol of covalently bound phosphate per mol of protein; SCBP contains no phosphate.