Evidence of a precursor form of stratum corneum basic protein in rat epidermis

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Abstract
Fully differentiated anucleate cells of the stratum corneum of newborn rat epidermis contain a cationic protein called stratum corneum basic protein (SCBP). This protein has MW (49,000) and an amino acid composition similar to a protein extracted from less differentiated cell layers of the epidermis. Pulse-chase experiments with radiolabeled histidine were undertaken to test the possibility that SCBP is derived from a preexisting protein. A protein of 52,000 daltons is rapidly but transiently labeled in extracts of less differentiated cell layers. As the amount of label in the 52,000 dalton protein decreases, radiolabel increase is observed in extracts of the fully differntiated cells. This label is found in SCBP, a protein of lower MW (49,00) than that initially labeled. These proteins are immunologically related and both are resistant to cyanogen bromide cleavage. They differ in apparent MW on sodium dodecyl sulfate-polyacrylamide gels and in net charge. Results are consistent with conversion of a precursor protein into SCBP.