Low Molecular Weight Ligands Bound to Zinc in Soybeen Seeds

Abstract

What kinds of ligand bind to zinc in soybean seeds has been investigated by using various fractionation methods. Homogenate of whole grains of soybean was separated into three layers by ultra-centrifugation, and a DEAE-cellulose ion exchange chromatography was applied to the separated middle later. The fractions in which Zn has eluted were collected and used as the sample of the following examinations. Free amino acids contained in the sample before (a) and after (b) acidhydrolysis were identified with a Hitachi's amino acid analyzer. By comparison of the amino acid pattern of the sample (a) to that of (b), the presence of peptides bound to zinc was suggested. Chemical form of the Zn-peptide complexes was discussed. A DEAE-Sephadex A-25 column chromatography was applied to the sample (a) and the elution of Zn, P, sugars and nucleotides was examined. On the elution profiles, two peaks at which the four species has eluted together were observed. The eluted sugar was identified to be a pentose and it existed on a bound type but not on free state. The eluted nucleotides were consisted of different two compounds of which absorption maxima exhibited at about 250 and 275nm, respectively. Two types of Zn-nucleotide complexes were considered as the possible compounds consisted of the four species. Their chemical forms were discussed. On the basis of the findings and the results reported previously, extensively discussion on the status of Zn in soybean seeds was attempted.