Fractionation and characterization of low molecular weight solubilized proteins of newborn rat keratohyalin granules.

Newborn rat epidermis was extracted using methods reported to extract keratohyalin granules. All extraction techniques yielded preparations of solubilized proteins with similar sodium dodecyl sulfate-polyacrylamide electrophoretograms. The solubilized proteins were fractionated on a Sephadex G-200 column and six low molecular weight protein fractions (apparent molecular weights between 10000 and 18000) have been identified. Four of these have been isolated and partially characterized. Two of the fractions are characterized by high histidine, arginine, serine and glutamic acid concentrations and have an amino acid composition similar to that of the histidine-rich protein characteristic of keratohyalin granules. One of these histidine-rich fractions (molecular weight 13700) has ribonuclease activity. The other two isolated fractions are basic proteins, one of which (molecular weight 12800) is a basic lysine-rich protein. This protein is not found in any other tissues of the new born or adult rat.