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Metabolism of Phosphatidylcholine in Freshly Secreted Milk¹

Department of Food Science, The Pennsylvania State University, University Park 16802

ABSTRACT

Phosphatidylcholines labeled with carbon-14 in the glycerol, the acyl groups, or uniformly labeled were incubated individually in freshly secreted goat milk from which fat globules were removed. After 2 h incubation at 37 C the milks were extracted to obtain the lipids, and radioactivities in the aqueous, neutral lipid, phospholipid, and free fatty acid fractions were determined. Activities in the phospholipid and neutral lipid fractions were resolved further by separation on thin-layer chromatographic plates and by assaying activity within the individual lipid classes. Evidence from all three labeled substrates showed that lipolytic degradation was the dominant metabolism during incubation. Free fatty acids, uncharacterized water-soluble products, and lysophosphatidylcholine were the principal products. Destruction of the labeled substrates ranged from 58 to 80%. Significant labeling of di- and triglycerides occurred in incubations with acylcarbon-14 and carbon-14 uniformly labeled substrates, presumably by incorporation of carbon-14 fatty acids released from those substrates. Carbon-14 labeled glycerol of phosphatidylcholine so labeled was incorporated poorly, if at all, into neutral lipids (di- and triglycerides) from the incubations.

¹ Journal Series No. 5362, Pennsylvania Agricultural Experiment Station.