Enzymatic activity of metal-binding proteins in epidermal cells

Enzymatic activity was investigated in metal-binding proteins from rat epidermal cells. Tris-HCl buffer soluble and KSCN solubilized proteins were extracted stepwise from granular and cornified cells of 2-day old rat epidermis. Each extract was separately applied to a Cu2+ or Zn2+ chelate Sepharose 6B column and the proteins were eluted with buffers of different pHs and finally with EDTA solution. Metal chelate-binding proteins were found in both soluble and solubilized proteins but there was a larger amount in the latter. Affinity of the proteins to bind with Cu2+ chelate was greater than that with Zn2+ chelate. In Tris-HCl buffer extract, histidase activity was detected in Cu2+ chelate-binding proteins, but not in Zn2+ chelate-binding proteins. Acid phosphatase, cysteine proteinase, dipeptidase, cathepsin D, beta-galactosidase, gelatin hydrolase, and superoxide dismutase did not bind to metal chelates although these enzymes, except acid phosphatase, were inhibited by Cu2+, but not by Zn2+. In contrast, KSCN solubilized metal chelate-binding proteins showed plasminogen activator, acid phosphatase, and gelatin and casein hydrolases while histone hydrolase did not bind to either chelate column. Since metal-binding proteins in rat epidermal cells have been shown previously to be histidine- and cysteine-rich proteins concentrated in keratohyalin granules, interaction of metals and the structural proteins with certain enzymes may be involved in the regulation of epidermal cell functions.