Apolipoproteins and the Association of Egg Yolk Proteins with Plasma High Density Lipoproteins after Ovulation and Follicular Atresia in the Rainbow Trout (Sulmo

The apolipoproteins of trout plasma lipoproteins have been characterized by sodium dodecyl sulfateglycerol polyacrylamide gel electrophoresis. The high density lipoproteins (HDL) (1.085 < d < 1.21 g/ml) contain four apolipoproteins, two major species with M, 25,000 (apoA-I-like) and M, 13,000 (apoA-11-like) and two minor species (M, 55,000 and 40,500). The very low density (d < 1.015 g/ml) and low density lipoproteins (1.015 < d < 1.085 g/ml) contain two high M, apolipoproteins (apoB-like) with M, 260,000 and 240,000 (the smaller is the preponderant species in low density lipoproteins), as well as a third apolipoprotein with M, 76,000. Type A apolipoproteins are present in the very low density lipoproteins, as are a group of apolipoproteins with M, 9,000-1 1,000 (apoC-like). Egg yolk proteins appear in the plasma of females about 30 days after natural ovulation or after that induced by salmon gonadotropin and during massive intraovarian atresias, either spontaneous or induced by 17~~,20&dihydroxy-4-pregnen-3-one. Two egg yolk proteins intimately associated with HDL have been identified. They may account for as much as 35% of total plasma proteins. Lipovitellin (M, 112,000) is composed of two subunits in a 1:l molar ratio (lipovitellin 1 with M, 92,000 and lipovitellin 2 with M, 20,000) and is present as a dimer with another yolk protein (M, 10,000). These results show that resorption of the yolk during follicular atresia in an oviparous vertebrate is correlated with the presence of egg yolk proteins combined with HDL in the plasma.