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

Rat liver cardiolipin, isolated by silicic acid column chromatography, has been resolved into five subfractions by discontinuous gradient elution from a silicic acid column. Comparison of these lipids with authentic beef heart cardiolipin established theis essential identity; the beef heart lipid differed only in having a more unsaturated fatty acid composition. A comparison between the five subfractions with regard to phosphorus and amino nitrogen content, ester/phosphorus ratios, fatty acid composition, infrared spectra, presence of salt forms, extent of peroxidation, component glycerphosphoric esters, and hydrolysis characteristics failed to explain the molecular basis for the fractionation. The presence of a free hydroxyl group in cardiolipin could not be confirmed by accetylation or acetonation. These observations were not consistent with the generally accepted diphosphatidyl glycerol structure for cardiolipin and lead to consideration of some additional possibilities.

The conversion of stearic acid to oleic acid has been studied in homogenates and other subcellular fractions of adipose tissues and liver of untreated and insulin-treated diabetic rats and rats maintained on a fat-free diet. The synthesis of the monounsaturrated fatty acid is an oxygenase reaction requiring molecular oxygen and DPNH or TPNH. The site of the reaction has been localized to the microsomes.

In diabetes, the microsomal enzymatic conversion of strearate to oleate stops. This defect in lipid metabolism, which is separable from the overall depression of lipid biosynthesis, is corrected by insulin therapy.

Behaviour of short-chain fatty acids located at C-2 of triglycerides in vitro and in vivo

Shorter-chain fatty acids located on the triglyceride internal carbon are quickly hydrolysed during lipolysis in vivo and in vitro. This hydrolysis is not due to a lack of positional specificity of pancreatic lipase (glycerol ester hydrolase, EC 3.1.1.3), but rather to a spontaneous migration of internal shorter chains towards outer positions in diglycerides and monoglycerides.

The migration of internal shorter chains has two important effects: (1) In vivo, the level of shorter chains in lymphatic triglycerides is relatively low, even when these' chains are internal in fed triglycerides. (2) In vitro, the well known technique using the positional specificity of pancreatic lipase for the determination of triglyceride structure cannot be applied when the internal chain of the triglycerides is hort.

The synthesis of cholesterol esters by plasma and extracts of acetone powders of rat plasma was studied with the following substrates: (a) lecithin labeled in the β position with either [I-¹⁴C]oleic acid, [I-¹⁴C]linoleic acid or [I-¹⁴C]palmitic acid; (b) trigylcerides labeled with either [I-¹⁴C]palmitic acid or [I-¹⁴]oleic acid; (c) [4-¹⁴C]cholesterol. As much as 24 and 50% of the incubated ¹⁴C was recovered as cholesterol esters when the labeled lecithins and free cholesterol, respectively, were incubated, and less than I% was so recovered when the labeled trigylcerides served as substrates. Snake venom completely prevented the formation of labeled cholesterol esters by acetone powder extracts in the experiments with fatty acid-labelled lecithin and the labeled free cholesterol. These findings support the hypothesis that the esterification of cholesterol is brought about by a fatty acid transferase and, in addition, suggest that the transesterification is limited to fatty acidss on the β position of phospholipids, regardless of the nature of the fatty acids, this being an intermediatry step even in the transesterification from trigylcerides.

• 1.

  1.The effects of glucose and a number of hormones on the incorporation of [1-¹⁴C]palmitic acid from the medium into glycerides in rat epididymal fat pads have been reported. The data from such studies should not, however, be used to draw conclusions about tha rate of triglyceride synthesis in this tissue.

• 2.

  2. It has been demonstrated that the free fatty acids in different cell fractions and in different parts of a single fat pad have different specific radioactivities after incubation of the intact fat pad in the presence of [1-¹⁴C]palmitate, suggesting that there are kinetically distinguishable pools of free fatty acids within the tissue.

• 3.

  3. Evidence is presented to support the view that free fatty acids from the medium can, as such, enter adipose tissue cells, and it suggested that there is a pool of free fatty acids, perphaps very small, within the tissue which serves as the precursor pool for glyceride synthesis.