No abstract

BWECKENR~GE, W. C., MAMI, L., AND KUKSIS, A. Triglyceride structure of human milk fat. Can. J. Biochem. 47, 761-7669 (11969).The triglycerides of the fat globules of human milk were resolved by thin-layer chromatography on silica gel impregnated with silver nitrate. The chemical structure of the glycerides was determined by gas chromatography of the glycerides and fatty acids and by a stereospecific analysis of total milk fat sampk. The major triglycerides of human milk fat contained 48-54 acyl carbons which were made up sf Ci2-Ffa acids of various degrees of unsaturation. The fully saturated triglywrides (6-873 contained mainly SPB-glycerol 1-stearate 2-palmitate esterified at position 3 with Cae-Cas acids. The monoensic triglycerides (25-2'6" %) were comprised mainly of sn-glycerol 1-oleate Zpalmitate esterified at position 3 t s Ci2-Cas acids, as well as their rammates. The dienes (2433%) were made up largely of sn-glycerol 1-stearate 2,3=dioleate and %-palmitate 83-diokate. The trienes (18-20%) contained mostly sn-glycerol 8,2,3-triokate and 1-sleate Zpalmitate 3-linoleate. The tetraenes (7-21 %) were identified as mainly S P B -~I~C~~O I 1 ,Zdioleate 3-linoleate and I -palmitate 2,3-dilholeate. Arachidsnic acid was found in the polyene fraction (6 %) in the Zpodtion, while the linolenic acid was preferentially associated with position 3 of the tetraenes.

1. To investigate differences between the metabolic effects of light and heavy exercise, five healthy males (mean maximal oxygen intake 3.92 litres/min) exercised for 40 min at 36% maximum power (light work) and 70% maximum power (heavy work) on separate days, after an overnight fast. 2. A steady state was achieved in both studies between 20 and 40 min in: oxygen intake (1.42 and 2.64 litres/min respectively); respiratory exchange ratio (0.89 and 1.01); plasma lactate concentration (1.78 and 9.94 mmol/l). 3. Plasma palmitate turnover rate (14C) was unchanged from resting values in light work but was decreased by 40% (from 104 +/- 16 to 63 +/- 8 micronml/min) in heavy work. Heavy work was associated with falls in the plasma concentrations of all free fatty acids measured: palmitic acid (C16:0), oleic acid (C18:1), stearic acid (C18:0), linoleic acid (C18:2) and palmitoleic acid (C16:1). 4. In contrast to th fall in palmitate turnover the increase in plasma glycerol was greater in heavy exercise (0.054-0.229 mmol/l) than in light exercise (0.053-0.094 mmol/l), suggesting that lipolysis was occurring which did not lead to influx of free fatty acids into plasma. 5. In light exercise fat metabolism may be controlled to favour adipose tissue lipolysis and extraction of free fatty acids by muscle from the circulation, whereas in heavy exercise adipose tissue lipolysis is inhibited and hydrolysis of muscle triglycerides may play a more important part. 6. The finding of a high respiratory exchange ratio may not exclude the use of fat as a major fuel source in exercise associated with lactate production.

The mature egg yolk of the domestic hen possesses remarkably constant lipid and lipoprotein composition despite much variation in dietary and environmental conditions. The greatest differences are seen in the fatty acid composition of the triacylglycerols which may show significant alterations in the content of the minor acids including certain polyunsaturated acids. The lipid class composition appears to be minimally affected by dietary influences, including the cholesterol content of the diet. The limited dietary influence on the yolk lipid composition extends to different strains of the hens. Genetic selection has led to some increase in the cholesterol content of the egg, but the desired lowering of the cholesterol content of egg yolk has not been realized. Likewise, production of a polyunsaturated fatty acid egg does not appear to be practical. As a result the egg yolk continues to provide a food product of nearly constant composition, which serves to maintain its chemical and physico-chemical properties for reliable utilization in the baking, cosmetic and pharmaceutical industries. The great uniformity in the composition of the egg yolk phospholipids makes them desirable starting materials for partial chemical resynthesis of glycerophospholipids. Partial hydrogenation of the egg yolk lipids promises to further increase the utility of the product as a desirable material for the manufacture of liposomes and liposome based drug products. In contrast, the constancy of the egg yolk composition and the inability to alter it significantly by dietary or genetic means also renders egg yolk undesirable for unlimited human consumption. Excessive ingestion of egg yolk raises plasma lipid and cholesterol levels which are believed to contribute to the development of heart disease. The physico-chemical and biological properties of egg yolk apoproteins have been less extensively investigated and their function is less well understood. The finding that phosvitin is a effective chelator of metal ions and thus an effective antioxidant demonstrates that egg yolk lipoproteins possess as yet unexplored potential for beneficial nutritional, medical and industrial application.

The enantiomeric nature of the triglycerides of bovine milk fat was reinvestigated by determining the stereospecific distribution of fatty acids in rearranged butterfat, following partial hydrolysis with pancreatic lipase, and in certain molecular distillates of native butterfat, following Grignard degradation. The results with rearranged butterfat confirmed the validity of pancreatic lipase hydrolysis as a means of generating representative diglycerides from milk fat triglycerides. The Grignard degradation and lipolysis gave identical distributions for fatty acids when included as part of the assay system in the stereospecific analysis. Characteristically, butyric acid and the other short chain acids occupied the 3 position in the native butterfat, while in the rearranged oil they were distributed more or less randomly. Gas chromatographic analysis of the short chain glycerides on polyester columns allowed an effective resolution of butyryl, caproyl and caprylyl glycerides of identical numbers of total acyl carbons and double bonds. The method was especially well suited for resolution of the 2,3‐diglycerides, which were recovered either as the more polar fraction from thin layer chromatography of the X‐1,2‐diacylglycerols, or by acetolysis of the residual phenolphosphatides resulting from phospholipase A digestion. It was shown that butyric acid in the 3 position was preferentially paired with myristic, palmitic and oleic acid in the 2 position, and palmitic and oleic acid in the 1 position, which was also characteristic of the other short chain acids.

A method is described for the separation, identification, and quantitative estimation of the individual molecular species occurring in natural lecithin mixtures. Purified lecithin preparations are converted into diglyceride acetates by enzymic dephosphorylation and acetylation. The diglyceride acetates are separated on the basis of the degree of unsaturation and the molecular geometry by means of chromatography on thin layers of silica gel which are impregnated with silver nitrate. The various acetates thus resolved are separately recovered from the plates and diluted with tridecanoin internal standard; the quantitative distribution of the molecular weights is determined by gas chromatography.Suitable aliquots of the saturated and unsaturated diglyceride acetates are further analyzed for over-all and for positional distribution of fatty acids. The identity and proportions of the various lecithins are deduced by integration and normalization of all the experimental data. Where doubt exists, specific diglyceride acetates are isolated by preparative gas chromatography, and their fatty acid composition is determined. The method is illustrated with data obtained for the mixed lecithins of egg yolk. The general approach is applicable to the determination of the structure of other phospholipids of comparable complexity.

Detailed investigation was made of the triacylglycerol structure of native, simulated, and interesterified peanut oils, which had previously been shown to differ markedly in their atherogenic potential. By means of chromatographic and stereospecific analyses, it was shown that the more atherogenic native oil contains a significantly greater proportion of triacylglycerols with linoleic in sn-2-position and arachidic, behenic, and lignoceric acids in sn-3-position that the synthetic oils. It is suggested that the atherogenicity may arise from a relative metabolic unavailability of the linoleic acid from the native oil, which may be due in part to the presence of long chain saturated acids in the outer position. This might render the oil metabolically more saturated that the interesterified oils of the same total fatty acid composition, which contain a much greater proportion of the linoleic acid in the primary postions of the triacylglycerol molecule. The identification of specific triacylglycerols may allow the experimental testing of this hypothesis by feeding synthetic triacylglycerols incorporating the potentially atherogenic features.

The molecular species of choline, ethanolamine, serine, and inositol phosphatides and triglycerides were determined in purified adenosine triphosphatase and in the parent sarcotubular membranes of rabbit skeletal muscle. The total membrane and the adenosine triphosphatase were essentially identical in the composition of lipid classes and closely similar in patterns of molecular species of the corresponding phosphatides and triglycerides. The phosphatidylcholines were made up largely of the 1-palmitoyl 2-oleoyl and 1-palmitoyl 2-linoleoyl species. The ethanolamine phospholipids contained mainly the plasmalogens 1-palmitaldehyde 2-arachidonoyl and 1-stearaldehyde 2-arachidonoyl along with smaller amounts of the 1-palmitaldehyde 2-oleoyl and 1-palmitaldehyde 2-linoleoyl species. The phosphatidylinositols, which were analyzed along with about 10% phosphatidylserine, were characterized by large proportions of 1-stearoyl 2-arachidonoyl and smaller but significant proportions of the 1-stearoyl 2-oleoyl, 1-stearoyl 2-linoleoyl, and 1-stearoyl 2-eicosatrienoyl species. The triglycerides contained significant proportions of tripalmitin, triolein, and the isomeric palmitoyl oleoyl linoleins.The composition and molecular association of the fatty acids in these phosphatides showed significant differences from that of other tissues of the rabbit and other animals, as far as they have been analyzed, except for phosphatidylinositol, the structure of which was similar to that found elsewhere. The triglyceride composition was unusual in the high content of simple triglycerides.