Egg Proteins

Egg yolk decreases the absorption of iron. The effects of egg yolk protein and egg yolk phosvitin on the absorption of calcium, magnesium, and iron were investigated by in vivo studies. Male Wistar rats were fed purified diets containing casein, soy protein, or egg yolk protein for 14 d. The apparent absorptions of calcium, magnesium, and iron in the rats fed the yolk protein-based diet were lower than those in rats fed the casein- and soy protein-based diets. The apparent phosphorus absorption and the apparent protein digestibility in the yolk protein group were lower than those in the casein and soy protein groups. In the feces of the yolk protein group, serine comprised more than 30% of the amino acids. The addition of egg yolk phosvitin to the casein diets at levels of 1% and 2% (w/w) produced effects on calcium and magnesium absorptions similar to those produced by the diet containing yolk protein. The tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern suggested that phosphopeptide fragments having molecular masses of 28, 22, and 15 kDa were evident in the contents of the small intestine of the rats fed phosvitin diets. These results indicate that yolk protein, when compared with casein and soy protein, decreases calcium and magnesium absorption via the resistance of phosvitin to proteolytic action.

Elucidation of a profile of scallop vitellin formation associated with oogenesis and its endocrine control, and identification of a vitellogenin synthesizing site were immunologically undertaken by using anti-scallop Vn serum. Vn content increased during ovarian growth and accounted for more than 80% of the water soluble protein of the ovary at the mature stage. In vivo injection of estradiol-17 beta (E(2)) resulted in an increase in Vn content in the ovary. In vitro accumulation of Vn in the ovarian tissue was promoted with E2 and a vitellogenesis promoting factor (VPF) from cerebral plus pedal ganglion which was heat stable, less than MW 10,000 and trypsin/chymotrypsin resistant. Estrogen receptor (ER)-like immunoreactivity was found in the growing oocyte and the auxiliary cell in close contact with growing oocytes, in which Vn immunoreactivity was also found. It is suggested that the vitellogenin synthesis occurred inside the ovary, especially in the auxiliary cell, and is contro...

The exuperantia (exu) gene of Drosophila melanogaster plays a fundamental role in the establishment of polarity of the oocyte and early embryo by ensuring the proper localization of the mRNA of the bicoid (bcd) gene to anterior regions of the oocyte. We have isolated and sequenced the exu gene, sequenced its female-specific transcript and a mutant allele of exu that affects primarily exu's female germline function, and determined the temporal and spatial pattern of exu protein expression during oogenesis. The exu protein is basic, with at least one basic residue being identified as necessary for exu function in the female germline, and is present transiently during oogenesis. Our results suggest that exu is not required for the maintenance of bcd mRNA localization during late stages of oogenesis and early embryogenesis, but rather for the establishment of bcd mRNA localization in the developing oocyte. We propose that the exu protein may serve to modify a component that binds bc...

A cDNA encoding a novel eggshell protein (OvESP) with high-glycine (49.2%) and -tyrosine (27.8%) content was cloned from the human liver fluke Opisthorchis viverrini. In the adult parasite, the RNA products of the OvESP gene are limited to the vitelline follicles. They have a size of 800 nucleotides and are already present in 2-week-old juveniles. Immune sera of hamsters, experimentally