Abstract
Partial hydrolyzate of zinc-casein (Zn 1.5%) was submitted to pH-fractionation and paper chromatography. Zinc was found to be distributed as a chelate compound in the peptides precipitating out in the pH range of (I) 7.2-7.4 and (II) 8.6-8.8 (Fig. 1). Further complete hydrolysis and the same procedures showed that (I) consists of leucine, tyrosine, glutamic acid, lysine, and a zinc-chelated amino acid (Fig. 2), and (II) of glutamic acid, lysine, and a zinc-chelated amino acid (Fig. 4). The zinc-chelated amino acids from (I) and (II) were isolated and removal of zinc afforded only histidine. The ultraviolet spectrum of zinc-chelated amino acid exhibits a maximum absorption at 266mμ, which disappears on removing zinc (Figs. 5, 6). Paper electrophoresis of zinc-chelated amino acid in alkaline buffer solution revealed that the compound remains in the original point, showing that the dissociation of zinc and histidine in aqueous solution does not occur.
