Epidermal protein synthesis in newborn rat skin.

Protein synthesis in newborn rat epidermis was assessed by in vivo labeling of epidermal proteins with radioactive glycine and the isolation of neutral buffer, sodium-dodecylsulfates (SDS) dithiothreitol soluble proteins, and 0.1 M NaOH soluble protein fractions of the epidermis. There was an increase in the labeling of proteins in the buffer and SDS fractions for 5 h after injection and then no further increase at 19 h after injection. In the 0.1 M NaOH soluble proteins and the final pellet after these extractions there was a progressive increase in glycine incorporation up to 19 h after injection. SDS gel electrophoresis of the labeled proteins showed early synthesis and continued synthesis of proteins of 56,000 and 65,000 daltons corresponding to the main fibrous proteins (alpha-keratins) of the epidermis. At 19 h a new protein band of 45,000 daltons first appeared and was associated with a decrease in the labeling of very high molecular weight (or highly aggregated) proteins. This later protein is presumptively identified as keratohyalin. Free amino acid pools were associated with both the neutral buffer and SDS extractable fractions.