Preparation, Properties, and Composition of Nereis vitellin, the Yolk Protein of the Annelid, Nereis virens

In the literature, oogenesis in nereid annelids is considered to be a model system because, unlike other system studied, nereid oocytes are thought to synthesize the bulk of their yolk protein themselves. As the first step to test the validity of this hypothesis, nereid yolk protein was characterized biochemically. Vitellin, the main fraction of the soluble yolk proteins, was prepared from Nereis virens oocytes. Preparation, purification, and some physical characteristics of this green-colored protein Nereis vitellin are described. The molecular weight was determined by gel chromatography as 420,000 daltons. With regard to the amino acid composition, Nereis vitellin was found to resemble both insect vitellins and an average protein, as defined by other authors. Methionine and cysteine were found in traces only. By staining procedures, Nereis vitellin was characterized as lipoglycoprotein. Nereis vitellin was also prepared from the coelomic fluid of gravid females of Nereis virens .