Composition and structure of phospholipids in chicken muscle tissues

Incorporation of ortho[32P]phosphate into phosphatidylcholines and phosphatidylethanolamines in rat skeletal muscle

1. The specific radioactivities of individual molecular species of muscle phosphatidylcholine and phosphatidylethanolamine have been measured by a combination of argentation thin-layer chromatography and countercurrent distribution. 2. The specific radioactivities of individual molecular species of muscle phosphoglycerides have been determined 3 h after intraperitoneal injection of ortho[32 P] phosphate. Under these conditions the specific radioactivities of the species present in rat muscle were found to be measures of the relative turnover times of these molecules. 3. The specificity radioactivity of phosphatidylcholine was approx. three times that of phosphatidylethanolamine. The 1-palmitoyl-2-oleoyl and 1-oleoyl-2-linoleoyl phosphatidylcholines had the fastest turnover and the 1-palmitoyl-2-arachidonoyl the slowest. Of the phosphatidylethanolamines, the linoleoyl and the docosahexaenoyl species showed the fastest turnover and 1-stearoyl-2-arachidonoyl the slowest. 4. The results indicate that phosphoglycerides in muscle turn over more slowly and more evenly than do liver phosphoglycerides.

Effects of dietary fat on the amounts and proportions of the individual lipids in turkey muscle

1. Lipid extracted from breast and leg muscle of 10-week-old turkeys was fractionated by preparative thin-layer chromatography and five individual ‘neutral’ and eight individual phospholipid fractions, representing 95% by weight of the extractable lipid, were recovered from the plates for analysis.

The ‘neutral’ lipids from breast and leg muscle consisted mainly of triglyceride (202–497 and 1644–2333 mg/100 g), together with cholesterol (74 and 103 mg/100 g), free fatty acid (27 and 123 mg/100 g), diglyceride (17 and 66 mg/100 g) and cholesterol ester (9 and 12 mg/100 g).

The phospholipids contained phosphatidylcholine (367 and 500 mg/100 g), phosphatidylethanolamine (157 and 279 mg/100 g), phosphatidylinositol (60 and 109 mg/100 g), sphingomyelin (43 and 62 mg/100 g), phosphatidylserine (31 and 61 mg/100 g), ‘cardiolipin’ (23 and 35 mg/100 g), lysophosphatidylcholine (9 and 11 mg/100 g) and ‘origin fraction’ (6 and 7 mg/100 g), accounting together (700 mg and 1070 mg/100 g for breast and leg muscle respectively) for 98% of the lipid phosphorus extracted.

Partial replacement of carbohydrate in the cereal-based diet by beef fat (2·5%) or anchovy oil (2·5 or 5·0%) had no effect on the amount of any of the lipid fractions, except for triglyceride, which varied considerably and was lowest in tissue from groups receiving 2·5% anchovy oil.

Effects of dietary polyunsaturated fatty acids on the composition of the individual lipids of turkey breast and leg muscle

1. Groups of turkeys were given, to 10 weeks of age: diets E, basal, containing 2.3% mainly cereal lipid; A, basal plus 2.5% beef fat; B, basal plus 2.5% anchovy oil; C, as B, plus 0.02% ethoxyquin; D, basal plus 5% anchovy oil. Lipids from breast and leg muscle of all five groups were fractionated by thin-layer chromatography into five ‘neutral’ and six phospholipid fractions and the fatty-acid composition of each was determined by gas–liquid chromatography.

2. Individual lipid fractions differed widely in fatty-acid composition and in the degree to which they could be influenced by dietary fat supplements. Small but usually consistent differences were observed between corresponding fractions from breast and leg. Sphingomyelin (SP) and lysophosphatidylcholine contained largely saturated acids (76–80%); the other phospholipids were 44–48% and the ‘neutral’ lipids 38–50% saturated. Phosphatidylserine (PS), phosphatidylinositol(PI) and, in less degree, phosphatidylethanolamine (PE) were rich in stearic acid, though palmitic was much more abundant in the diets and in the other muscle lipids. SP contained no acid more unsaturatedthan linoleic (1–2%). PE and PI were richest in arachidonic and PE and PI in other polyene acids.

3. The effects of beef fat on the muscle lipids were small and mainly on the ‘neutral’ fractions.

4. The polyunsaturated fatty acids of the fish oil extensively displaced linoleic (and oleic) acids from all fractions (except SP); arachidonic acid was displaced from PE but not from PI.

5. The degree to which the fish-oil polyunsaturated acids of the three series entered the muscle lipids varied with the acid and with the fraction. Docosahexaenoic acid (22:6) reached a concentration of 20–25% in PE, nearly five times as great as its concentration in the dietary lipid.

6. Hydrolysis with phospholipase A showed that most of the unsaturated fatty acids were present in the 2-position of PC and PE, but the positional specificity was not complete, particularly for the less highly unsaturated acids.

7. The antioxidant ethoxyquin had no effect on the fatty-acid composition of any of the muscle lipid fractions.