Isolation, purification and characterization of the egg-yolk proteins from the oocytes of the Indian freshwater murrel, Channa punctatus (Bloch).

In oviparous organisms, yolk accumulation in the oocytes is critical and indispensable for the development of the newly hatched young ones. In fish and many other oviparous vertebrates, the major constituents of the egg-yolk are synthesized as a precursor in the liver. The precursor is transported to the oocyte for uptake and cleaved into major yolk proteins lipovitellin, phosvitin and β’-components. The eggs of Channa punctatus are pelagic, have large oil globule and exceptionally high lipid content. Lipovitellin was isolated by single step gel filtration chromatography on Sepharose 6B. Purified native lipovitellin showed immunological reactivity with vitellogenin antiserum. Phosvitin isolated by phenol extraction method could not be visualized with routine protein staining methods, whereas incorporation of trivalent ions in the coomassie brilliant blue stained phosvitin. It was characterized by in vivo labeling of egg-yolk proteins with 32P. The molecular mass of murrel phosvitin was less than 14,000 kDa.

Isolation and identification of yolk proteins in Indian major carp, Labeo rohita.

Two yolk proteins (YP1 and YP2) from the ovaries of Indian major carp, Labeo rohita were isolated by gel filtration and partially characterized by the use of hydroxyapatite ultrogel column in conjunction with native PAGE. On native PAGE YP1 gave a single protein band, whereas YP2 of gel filtration revealed the contamination of YP1, which was removed by adsorption chromatography on hydroxyapatite ultrogel and then the YP2 was the purified one as judged by electrophoresis. Both YP1 and YP2 also stained for lipid and contained alkali-labile phosphorus. Therefore, both yolk proteins were lipophosphoprotein. The molecular weights of YP1 and YP2 were 620 kDa and 225 kDa respectively as determined by gel filtration on Sepharose 4B. When YP1 and YP2 were compared in relation to some physicochemical characteristics with yolk proteins of other oviparous vertebrates including fish, they were lipovitellin like. Antiserum to YP2 crossreacted with YP2 and vitellogenin suggesting that YP2 was the cleaved product of vitellogenin. Anti-YP2 antiserum was not crossreacted with native YP1, whereas reduced and/or denatured YP1 was crossreacted indicating the presence of antigenic determinants in the inner core region of YP1 polypeptide.