A lipophosphoprotein complex in hen plasma associated with yolk production

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Abstract
A lipophosphoprotein complex (PLP) of constant composition can be precipitated from laying-hen plasma by dilution with water, and a method for its preparation and estimation has been developed. It is not detectable in the plasma of non-laying hens or of cocks. The concentration of PLP is about 2 g/100 ml of plasma and is very variable. It consists of about 20% of protein and 80% of lipid (of which 25% is phospholipid and 4% is cholesterol, largely free). The remaining lipid is probably largely or wholly triglyceride. The protein contains approximately 0.75% of P (80% of which is very labile to alkali, indicating that it is phosphoprotein). PLP accounts for a large but variable proportion of whole plasma lipids; i.e. total lipid, about 80%; phospholipid and cholesterol, approximately 65%. It also accounts for about 35% of the plasma protein P and 10% of the protein N. PLP appears in hen plasma about 7 days before the first ovulation and disappears within a few days when hens go off lay. The plasma concentration and composition of PLP during these periods have been examined. Details of changes in the lipid and protein N and P of the supernatant obtained from the preparation of PLP are also given. Preliminary ultracentrifugal analysis of PLP has shown it to consist of 2 components. The major one floats in a NaCl solution of specific gravity 1.006, with an apparent S - 11, and the other sediments (apparent S 13). It is possible that PLP transports most of the plasma lipid and almost half the plasma phosphoprotein included in egg yolk.