Biochimica et Biophysica Acta (BBA) - Specialized Section on Lipids and Related Subjects最新文献

• 1.

  1. Evidence for the intact utilization of 2-monopalmitin for triglyceride biosynthesis by the intestine has been obtained.

• 2.

  2. The enzymes catalyzing the conversion of both the 1- and 2-monoglycerides to triglycerides reside primarily in the microsomes.

• 3.

  3. One enzyme, monoglyceride trasacylase (acyl-CoA:monoglycerides acyltransferase), accepts both the 1- and 2-isomers.

• 4.

  4. The enzyme demonstrates a preferential utilization of the 2-monoglyceride.

• 5.

  5. The interrelationships of the reported finding to the absorption of fats is presented.

• 1.

  1. Rats were fed [¹⁴C]tripalmitin and guinea-pigs injected with ¹⁴C-labelled chylomicrons and the livers examined at various time intervals. Most of the ¹⁴C was associated with the individual liver cells but up to 43% of the total in the tissue could be free of the cells.

• 2.

  2. Isolated rat-liver cells can bind chylomicrons to the extent of 40 μg lipid per mg tissue N.

• 3.

  3. The bound chylomicrons are hydrolysed to give free fatty acids.

• 4.

  4. The fatty acids produced are firmly bound but can be removed by fatty acid-free albumin, suggesting that hydrolysis occurs at the cell surface.

• 5.

  5. The hydrolysis of chylomicron triglyceride is not inhibited by protamine sulphate or by heating the cells at 60°; nor is it stimulated by taurocholate.

The NADP-dependent malate dehydrogenase (decarboxylating) (l-malate: NADP oxidoreductase (decarboxylating) EC 1.1.1.40), combined hexose monophosphate shunt dehydrogenases^∗ and isocitrate dehydrogenase (l_S-isocitrat: NADP oxido-reductase (decarboxylating), EC 1.1.1.42) activities were assayed in mitochondrion-free fractions of liver obtained from normal fed, starving, starving but X-irradiated, and refed rats. Starvation for 48 h decreased the first two enzyme activities to about half that of the normal liver, whereas refeeding for 48 h with carbohydrate rich diets after starvation increased these enzyme activities over five times the normal liver value. In starving but X-irradiated (2400 R) rats the combined hexose monophosphate shunt dehydrogenase activity was similar to, and malate dehydrogenase (decarboxylating) activity was higher than, those of normal fed liver. There was no such marked effect of these experimental conditions on the isocitrate dehydrogenase activity which remained relatively unaltered. Compared with liver, in epididymal fat pads of normal rat the combined hexose monophosphate shund dehydrogenases, malate dehydrogenase (decarboxylating) and malate dehydrogenase (l-malate: NAD-oxidoreductase, EC 1.1.1.37) were considerably more active, whereas lactate dehyrogenase (l-lactate: NAD oxidoreductase, EC 1.1.1.27) and isocitrate dehydrogenase were less active. Thus in addition to the dehydrogenases of hexose monophosphate shunt, malate dehydrogenase (decarboxylating), but not isocitrate dehydrogenase, showed a close association with lipogenesis. Malate dehydrogenase (decarboxylating) is conceivably involved as a source of NADPH₂ formation. Experimental evidence is presented for the conversion of NADH₂ to NADPH₂ in preparations from liver and epididymal fat pads which involve malate dehydrogenase (decarboxylating) and malate dehydrogenase.

• 1.

  1. The rapid incorporation of label from intravenously administered serum-bound 9(10)-mono- and 12-monohydroxystearic acids into palmitic, stearic and octadecenoic acids in the intact rat has been demonstrated.

• 2.

  2. Analysis of label distribution in the newly formed non-hydroxy acids, following different labeling of the injected monohydroxystearic acids, indicates that breakdown to, and resynthesis from, acetate accounted for this conversion.

• 3.

  3. No evidence was found for a specific dehydration of monohydroxystearic acids to the unsaturated analogs.

• 4.

  4. The monohydroxystearic acids were extremely rapidly broken down: less than one-fifth could be recovered as such from the whole rat 5 min after intravenous injection.

Differences in phospholipid distribution and fatty acid composition between erythrocytes of different mammalian species, were investigated by dietary experiments with rats and sheep. The nature of teh ingested fats, and the non-participation of the ruminal micro-flora, appeared not to affect the proportions of the majro phospholipid classes in the erythrocytes studied. The differences in the composition of fatty acid constituents of red-cell phospholipids were shown to the attributed both to different dietary habits, ruminal processes and species differences in the biosynthesis of fatty acids.

The physical and chemical properties of the carotenoid pigments of Micrococcus lysodeikticus have been determined. Following saponification, at least seven different pigments can be separated by column-chromatographic procedures. These pigments have similar absorption spectra but differ in polarity. The absorption spectra of these bacterial pigments are similar to those of the carotenoid neurosporene. Polar pigments predominate and no hydrocarbon carotenoids have been detected.

Absorption maxima, partition coefficients, reaction to I₂ and acids and melting points were determined.

The nature of the polar groupings present in these pigments and their relation to other bacterial pigments are discussed.

• 1.

  1. A mechanism is proposed to account for the rapid cessation of fatty acid synthesis in the lactating mammary gland following weaning. It is suggested that milk contains an inhibitor which accumulates with the retained milk and serves to shut off fatty acid synthesis.

• 2.

  2. Extracts of lactating rat mammary glands were prepared at various time intervals from 3 to 24 h following weaning. During this period there is a rapid accumulation of milk in the gland, measured by the lactose concentration in the extract and a concomitant diminution of fatty acid synthesis, measured by the incorporation of [¹⁴C]acetate into long-chain fatty acids. Fatty acid synthesis is partially restored in such extracts if the rat, whose young were removed 24 h previously, is sucked by another litter for 3–18 h, resulting in the removal of all the accumulated milk from the gland.

• 3.

  3. When access to some of the rat's mammary glands is prevented for 9 h while the other glands are suckled, milk accumulates in the obstructed glands. Extracts from such glands incorporate only one-tenth as much [¹⁴C]acetate into fatty acids as extracts from the suckled glands.

• 4.

  4. The addition of rat milk to an extract of actively lactating rat mammary gland results in severe inhibition of fatty acid synthesis.

• 5.

  5. Acetyl-CoA carboxylase (acetyl-CoA:CO₂ ligase (ADP), EC 6.4.1.2) was measured in (NH₄)₂SO₄-treated mammary extracts by the incorporation of NaH¹⁴CO₃ into malonyl-CoA. This enzyme is profoundly inhibited by the addition of rat milk.

• 6.

  6. The inhibitory activity is located in the particulate fraction of milk.

A chromatographic study has been conducted on the lipid components of the food of queen larvae (royal jelly) of the honeybee, Apis mellifera L. In addition to previously characterized decanoic acid derivatives, this material is shown to contain small amounts of a number of uncharacterized hydroxy acid components, two of which have been isolated in crystalline form. The chromatographic properties of a number of decanoic acid derivatives are described. A useful relationship between retention time on gas-liquid columns and structure of the substituted decanoic acid derivatives, similar to the relationship described by Clayton for sterol derivatives, is discussed.