XENOPUS LIPOVITELLIN-1 IS A ZN2- AND CD2+-BINDING PROTEIN()

This report discusses the identification of a Zn2+- and Cd2+-binding p rotein of Xenopus laevis that is abundant in vitellogenic oocytes and in embryos from fertilization to stage 46. Oocyte or embryo homogenate s were fractionated by SDS-PAGE, blotted onto nitrocellulose, and prob ed with Zn-65(2+) or Cd-109(2+). The resulting autoradiograms showed b inding of both radionuclides to a protein, designated pCdZn. Freon ext raction of oocyte and embryo homogenates showed pCdZn to be a yolk pro tein. When pCdZn was isolated from oocyte homogenates by ammonium sulf ate precipitation, delipidation, and chromatography, it co-purified wi th lipovitellin 1. The amino acid composition of pCdZn closely resembl ed the reported composition of lipovitellin 1 and the molecular weight of purified pCdZn (similar to 115 kD) corresponded to reported values for lipovitellin 1 (111-121 kD). Amino acid sequence analyses of five peptides derived from pCdZn yielded 94% identity to the reported sequ ence of lipovitellin 1, deduced from the DNA sequence of the Xenopus v itellogenin A2 precursor gene. Based on these findings, pCdZn was iden tified as lipovitellin 1. This study suggests that lipovitellin 1 is t he major storage protein for zinc in mature oocytes and developing emb ryos of Xenopus laevis. (C) 1995 Wiley-Liss, Inc.