The nature of protein in the immature egg yolk of rainbow trout was investigated. There exist three components in the proportion of 84.0, 11.6, and 4.4 per cent in the yolk.
Among these three components the principal one, component I, was a kind of lipoprotein. It contained 11.9 per cent of nitrogen, 0.5 per cent of phosphorus, a little carbohydrate, and 22.8 per cent of lipid of which some 50 per cent was phospholipid.It is noteworthy that this lipoprotein-like substance was deficient in carotenoid pigment.
The component 11 was an unidentified protein composed of 12.7 per cent of nitrogen and less than 0.1 per cent of phosphorus.
The component Ill was a phosphoprotein soluble in water. It contained 8.2 per cent of phosphorus and 14.3 per cent of nitrogen.