Four cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions, respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible for 9,10-desaturation.

The mechanism of the hardening of body fats of animals by dietary lipids which contain cyclopropene fatty acids has been studied. Dietary methyl sterculate increased the stearic acid content of egg yolk lipid and decreased the activity of the stearic acid desaturase system of hen liver. The cyclopropene fatty acids were specific inhibitors of the stearic acid desaturase system of hen livers since other fatty acids, including two possible metabolites of sterculic acid, failed to inhibit the system at equivalent concentrations. Sterculic acid was a more effective inhibitor of the system than malvalic acid. Kinetic studies have shown that the inhibition is irreversible. Apparent kinetic constants were determined for the system.The results support the hypotheses that cyclopropene fatty acids inactivate an essential component of the desaturase system, probably by combination with-SH groups, and that this inhibition causes many of the effects of dietary cyclopropene fatty acids, including permeability disorders of eggs.

The effects of heating at 132°C on the fatty acids and fatty aldehydes of neutral lipids and phospholipids of lean beef, veal, lamb, pork and chicken were studied. Heating caused hydrolysis of the plasmalogens in the phospholipids, and varying amounts of the liberated fatty aldehydes were recovered in the neutral lipid fractions. Beef phosphatidy1 choline lost more polyunsaturated fatty acids than that of the other meats. Beef and veal phosphatidyl ethanolamine lost more polyunsaturated fatty acid than that of lamb, pork or chicken, but the effect was obscured by the influx of fatty acids from elsewhere into this fraction after heating.

The ethanolamine phospholipids of beef, lamb, pork and chicken examined in this study contained over 40% of ethanolamine plasmalogen, whereas fish contained only 13%. The level of choline plasmalogen in choline phospholipids was less than 1% in fish and ranged from 10 to 30% in the other four meats. Palmitaldehyde was the major fatty aldehyde in the choline plasmalogens of beef, lamb, pork and chicken (6580% of total aldehydes), but was present at lower levels in the ethanolamine plasmalogens. The per cent fatty acid compositions of phosphatidylethanolamine and the corresponding ethanolamine plasmalogen were very similar, being typically low in palmitic acid but very high (56-74%) in polyunsaturated fatty acids. The fatty acids of the choline plasmalogens contained more polyunsaturated fatty acids than the corresponding phosphatidyl cholines, but at lower levels than in the fatty acids of the ethanolamine phospholipids. KeywordsCholine plasmalogen, ethanolamine plasmalogen, fish lipids, palmitaldehyde, poultry meat lipids, red meat lipids.

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