Heterogenous proteins in keratohyaline granules studied by quantitative autoradiography

Electron microscopic autoradiography with [3H]histidine, [3H]cystine, I13H]arginine, and [3H]proline was used to study protein synthesis in keratohyaline granules of newborn rats. All 3H-amino acids were incorporated into proteins in the granular cells, and the radioactive proteins appeared in the keratohyaline granules. However, the amount of radioactivity associated with the granules and the pattern of ultrastructural localization of the radioactive proteins differed considerably for each 3H-amino acid. "Histidine-labeled" protein was located mainly in the matrix portion of keratohyaline granules whereas "cystine-labeled" protein accumulated in the dense homogenous deposits. "Arginine-labeled" protein was distributed more diffusely in the organelles of granular cells, but that associated with keratohyaline granules seemed to localize mostly with "histidine-labeled" protein and partly with "cystine-labeled" protein. Large amounts of "proline-labeled" protein were also present in other areas of the cytoplasm than keratohyaline granules. This protein localized in the dense homogeneous deposits, but it seemed to turn over more rapidly than "cystine-labeled" protein, an indication that the dense homogenous deposits consist of at least two different polypeptide chains, one of which contains higher cystine and the other higher proline.