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Previous studies from this laboratory revealed that phosphatidyl serine (PS) isolated from plate-let phospholipid extracts by silicic-acid column chromatography could replace blood platelets in tests of thromboplastin generation and prothrom-bin consumption of platelet-poor "native" plasma (1, 2). When rigorous criteria of identification were employed, it was found that phosphatidyl ethanolamine (PE) fractions contained traces of PS (2); coagulant properties were therefore difficult to evaluate. Rouser, O'Brien, and Heller (3) recently accomplished the complete separation of PE from PS by means of a double column technique using silicic acid and ammoniated silicic acid. Their studies were carried out on lipids of beef brain, but the methods could be applied to human brain and platelet extracts. In 1961, an earlier study of the fatty acids of platelet phosphatides with gas-liquid chromatography was reported (4). PE and PS were then, of necessity, studied as a combined fraction, and similarly the choline phosphatides were not adequately separated. In addition, the significance of oxidative changes consequent to prolonged separations and exposure of phospholipids to air was not appreciated, a factor which influenced the overall results. Zilversmit, Marcus, and Ullman (5) reported that 16 per cent (dry weight) of total platelet lipid extracts were in the plasmalogen form (phos-pholipids that liberate higher fatty aldehydes on hydrolysis). It could not, however, be determined how the plasmalogen was distributed among individual phosphoglycerides, although it was known (2) that the b)ulk of plasmalogen was associated with the combined PEPS fractions. When methyl esters of fatty acids of phosphoglycerides are formed, the aldehydogenic chains of plasmalo-gens are simultaneously converted to dimethyl-acetals. These derivatives can be separated from methyl esters on polar and nonpolar gas-liquid chromatographic columns (4, 6, 7), thus affording an additional qualitative and quantitative measurement of plasmalogen to supplement other analytical methods (5). In the present study, human platelet PE and PS were separated by techniques that minimized oxi-dative changes, which permitted an accurate evaluation of the activity of these lipids in different blood clotting systems. In addition, it was possible to carry out a detailed study of the fatty acid and fatty aldehyde composition of platelet phos-phatides by gas-liquid chromatography. MATERIALS AND METHODS In order to standardize and insure reproducibility of the extractions, separations, and coagulation tests, 8 preliminary runs were performed with lipids of fresh, human brain tissue. The main data to be presented are the findings of 7 similar runs with human platelet material. Although …

PLATELET PHOSPHATIDES. THEIR FATTY ACID AND ALDEHYDE COMPOSITION AND ACTIVITY IN DIFFERENT CLOTTING SYSTEMS*