ULTRACENTRIFUGAL ANALYSIS OF YOLK PROTEINS IN RAINBOW TROUT EGG AND THEIR CHANGES DURING DEVELOPMENT

Yolk proteins in Salmo irideus (rainbow trout) eggs were studied by means of ultracentrifugal analysis, and the following facts were clarified. Unfertilized eggs contain two protein components, designated as component I (90% in relative content) and component II (10%). The sedimentation constant for component I is 9.4 S and its molecular weight is approximately 240,000 ~ 260,000. The phosphorus and lipid contents of this major component are similar to those of a lipovitellin in hen's egg yolk, but the molecular weight is considerably smaller than that of the hen's lipovitellin. Component I is split by alkali into two subunits. The sedimentation coefficient for the subunits is 4.9 S and the molecular weight is approximately 120,000. The sedimentation coefficient for component II is 3.1 S, and the phosphorus content is higher than that of component I but is lower than that of hen's phosvitin. A new component of 11.2 S appears at the beginning of the eyed stage, and is inferred to be a protein in the blood formed at this stage. The relative changes of these three components during the synchronous development of embryo from fertilization to the swim-up fry stage were followed.

STUDIES ON THE LIVETINS OF HEN'S EGG YOLK: II. IMMUNOELECTROPHORETIC IDENTIFICATION OF LIVETINS WITH SERUM PROTEINS

Ten antigens have been distinguished in the sera of cocks and non-laying hens by immunoelectrophoretic analysis (IEA) against homologous rabbit antisera. An additional antigen has been found in the sera of laying hens by IEA against anti-laying-hen serum.Four of the serum antigens obtained by IEA have been correlated electrophoretically with the filter paper electrophoretic fractions serum albumin, serum α2-globulin, serum β-globulin, and serum γ-globulin.Serum albumin, serum α1-globulin, serum β-globulin, and serum γ-globulin have been identified immunologically with alpha-livetin, a livetin antigen (livetin 2), gamma1-livetin and gamma2-livetin respectively. Another antigen of cock serum and hen serum has been identified by IEA with a livetin antigen detected by IEA of livetin against anti-cock, anti-hen, and anti-yolk sera.

CHROMATOGRAPHIC SEPARATION OF PHOSVITIN, α- AND β-LIPOVITELLIN OF EGG YOLK GRANULES ON TEAE-CELLULOSE

The two components of lipovitellin and the three major components of yolk granules, phosvitin, α- and β-lipovitellin, have been separated by gradient elution chromatography on TEAE-cellulose. A 0.2 M phosphate buffer (pH 6.8) had the necessary ionic strength to dissolve these proteins and when applied in this solvent all components except β-lipovitellin were retained by the column. A linear gradient of ionic strength (limit buffer 0.2 M phosphate plus 0.5 M NaCl) was used to remove the other components. Recovery was essentially complete and the composition and properties of the individual components were similar to those obtained by previous chromatographic methods that gave only partial recovery. An additional component eluted after α-lipovitellin and before phosvitin, previously observed in Dowex-1 separations, was also observed by the present method. The composition, sedimentation behavior, and absorption spectra of this component indicate that it is a soluble complex of phosvitin and lipovitellin. When granules are dissolved in alkaline solvents (pH 9.4) of low ionic strength (0.05), phosvitin is not evident as a separate component during ultracentrifugation, but appears as the ionic strength is increased.

STUDIES ON THE LIVETINS OF HEN'S EGG YOLK. I. IDENTIFICATION OF PAPER-ELECTROPHORETIC AND IMMUNOELECTROPHORETIC LIVETIN FRACTIONS WITH SERUM PROTEIN ANTIGENS BY IMMUNOELECTROPHORETIC ANALYSIS

Immunoelectrophoretic analysis of an egg yolk livetin preparation has demonstrated the presence of six distinct fractions, which were numbered 1, 2, 3, 4, 5, and 6 from the anodic end of the electropherogram. Four of these fractions have been identified with four livetin fractions obtained by paper electrophoresis as follows: immunoelectrophoretic fraction 1 with alpha-livetin, fraction 2 with beta-livetin, fraction 4 with gamma1-livetin, and fraction 5 with gamma2-livetin.Immunoelectrophoresis of hen serum or cock serum against antilivetin serum has shown that both hen and cock sera contain antigens electrophoretically and immunologically identical to alpha-, beta-, gamma1-, and gamma2-livetins.

FRACTIONATION AND DISSOCIATION OF THE AVIAN LIPOVITELLINS AND THEIR INTERACTION WITH PHOSVITIN

Phosvitin and lipovitellin, the granule proteins of hen's egg yolk, were clearly separated by gradient elution on Dowex-1 columns. No phosvitin could be detected in the lipovitellin fraction but the first eluates of the phosvitin fraction contained lipovitellin of high protein phosphorus content. These initial eluates contained only two components sedimenting at rates slightly higher than dimer and monomer lipovitellin. As the lipovitellin monomer does not ordinarily occur in neutral solvents, the slower sedimenting material is either a new component or the monomer stabilized through interaction with phosvitin.Gradient elution chromatography of the total lipovitellins on hydroxyapatite showed that β-lipovitellin was completely eluted by 0.6 M phosphate buffer at pH 6.8 and appeared to be homogeneous. However, α-lipovitellin was heterogeneous: it was eluted over a concentration range of 0.7 to 1.4 M and the protein phosphorus content and dissociative behavior of successive fractions showed a progressive change with increasing ionic strength. Superimposed on this general heterogeneity of α-lipovitellin, there was consistent evidence of two poorly defined components, and three when the α-fraction was rechromatographed. Following dissociation and reassociation, there was no evidence of hybridization between monomers of α- and β-lipovitellin. Changes in the chromatographic patterns of α-lipovitellin following dissociation may indicate hybridization of different α-monomers, but these could also arise from structural changes in the monomers.

Isolation and composition of avian egg yolk granules and their constituent alpha- and beta-lipovitellins

The yolk granules from hen's egg represent on a dry basis 23% of the yolk solids, and they contain about 90% of the protein phosphorus, 95% of the iron, and nearly 70% of the calcium in yolk. Ultracentrifugal and other analyses on solutions of the granules show that they are 70% α- and β-lipovitellin in an approximate ratio of 1:1.8, 16% phosvitin, and 12% low-density lipoprotein. The properties and composition of the two lipovitellins isolated from the granules are the same as those isolated from solutions of whole yolk. Further purification reduces the protein phosphorus in α-lipovitellin to 0.50% and in β-lipovitellin to 0.27%, and this confirms that α-vitellin has a higher phosphorus content. Experiments at low temperature suggest that phosvitin exists in the granules as a high molecular weight complex.