Sulfur-containing Proteins and Epidermal Keratinization

Sites of synthesis of sulfur-containing protein in keratinizing epithelium have been studied by radioautography after injection of sulfur-labeled cystine. Bern et al. (3) demonstrated concentration of silver grains immediately below the cornified layer, suggesting that much of sulfur is added at the final stages of keratinization as observed in hair. In contrast, B6langer (4) reported that protein synthesis occurs mainly in the Malpighian cells, and Hoober and Bernstein (17) reached a similar conclusion. Radioautographs prepared with beta emission of sulfur 35 lack resolution, and determination of precise localization of radioactivity with sulfur 5 becomes very difficult because of its greater energy (167 Kev) compared to that of tritium (18 Kev) (24). In addition, light microscopy alone is not sufficient to study distribution and movement of newly synthesized protein,