ORGANIZATION AND COMPOSITION OF THE AMPHIBIAN YOLK PLATELET. II. INVESTIGATIONS ON YOLK PROTEINS

¹ Department of Biology, New York University, New York 53, N. Y.

1. Washed yolk platelet suspensions (prepared from ovarian eggs of Rana pipiens) lyse in the proper concentrations of NaCl or CaCl₂, resulting in solubilized yolk (YP_na or YP_ca) and an insoluble "ghost" residue. Different precipitation effects result with NaCl and CaCl₂ at lowered salt concentrations.

2. A compact precipitate (YC) resembling yolk platelets in density and volume results from a reduction of the salt concentration of YP_na to 0.28-0.30 M NaCl. A further reduction in salinity transforms YC from a plastic to a rigid material.

3. About 10% of the dry weight of soluble yolk is readily extracted with 9.6% ethanol: ether without affecting the solubility properties of the yolk proteins. The extracted lipids contain all or most of the yolk carotenoids, primarily xanthophylls.

4. Electrophoretic analyses show yolk fractions precipitated from YP_na by dilution (YP, YC, and WC) to be similar. Lipid-extracted yolk (YP_df) also gave a similar electrophoretic pattern.

5. Differences between the phosphorus/nitrogen ratios of whole yolk suspension and YP_na (0.14) and "ghost" material (0.20-0.21) support the conclusion that "ghost" material is largely non-yolk in origin.

6. Both DNA-P and PNA-P are detected in washed yolk platelet suspension and in soluble yolk, but the quantity found varies among different batches of yolk. The amount of DNA-P in some preparations is sufficient to account for the excess DNA/egg reported by previous investigators.

7. A minimum of 5 antigens are found for solubilized yolk, using both rabbit and chicken antisera. "Ghost" material shows three antigens in common with soluble yolk.