Purification and characterization of vitellin from the ovaries of the shrimpMetapenaeus ensis(Crustacea: Decapoda: Penaeidae)

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Abstract
Vitellin from the ovaries of the shrimp Metapenaeus ensis was isolated using gel filtration and anion exchange chromatography. Gel filtration revealed the presence of three peaks in an extract of mature ovaries. Two of these peaks were hardly noticeable in ovaries from immature shrimp. One of these was identified to be vitellin based on the results of Sudan black B and PAS staining for lipoprotein and glycoprotein, respectively. Purified vitellin with a molecular weight of 350 kD was composed of four subunits as revealed by SDS-PAGE. The two major subunits exhibited a molecular weight of 76 and 102 kD, respectively. Amino acid analysis of native vitellin revealed that glutamate/glutamine, alanine, valine and aspartate/asparagine were the major residues. A comparison with the amino acid compositions of vitellins reported for other penaeids shows that there are no great differences among penaeids. Vitellin from M. ensis demonstrated an isoelectric point of 5.0 because of a high level of acidic amino acid residues. It possessed a lower level of arginine (0.96%) and threonine (0.14%) residues when compared to vitellins of other penaeids.