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

• 1.

  1. The intact utilization of 1-monopalmitin by intestinal mucosal enzymes for the synthesis of triglycerides has been demonstrated.

• 2.

  2. The enzyme does not demonstrate a specificity for the d or l isomer

• 3.

  3. The first acylation of 1-monopalmitin occurs at the corresponding pirmary hydroxy group forming the 1,3-diglyceride intermediate.

• 4.

  4. The subcellular location and optimal requirements of the enzyme system catalyzing the acylation have been determined.

• 1.

  1. A particulate system obtained from lactating-goat mammary gland catalyzed the incorporation fo [I-¹⁴C]acyl-CoA into glycerides with dl-α-glyceroophosphate or α,β-diglyceride as acyl acceptor.

• 2.

  2. The pathway for the triglyceride synthesis in this system appears to involve the formation of diglyceride form α-glycerophosphate and its subsequent conversion to triglyceride.

• 3.

  3. Oleic, hexanoic, octanoic, and palmitic acids were incorporated into glycerides to different but considerable extents while the incorporation of butyrate was relatively low.

• 4.

  4. The incorporation of palmitate into α-glycerophosphate resulted in the formation of considerable proportion of triglycerides. On the other hand, the incorporation of hexanoate or octanoate into α-glycerophosphate did not proceed beyond the formation of diglycerides to any appreciable extent.

• 5.

  5. Utilization of glycerol for glyceride synthesis was not appreciable in this system.

The isotopic equilibrium method using [4-¹⁴C]cholesterol has been applied on female rats and their progeny. It has been possible to determined the quantities of exogenous and endogenous cholesterol, of fixed (inert) and exchangeable cholesterol, and of exchangeable cholesterol of endogenous origin present not only in a entire rat at different growth stages from the 12th day of foetal life to the adult state, but also in certain of its organs (liver, brain, skin …). These results together with complementary experiments have made possible the determination of the fractional rates of appearance (exogenous and endogenous), of increase and of turn over of exchangeable cholesterol during the growth of the rat.

The most outstanding features of this metabolism are the following: (1) All fixed cholesterol is of synthetic origin. (2) The proportion of exchangeable cholesterol falls with age to the adult value (50–55%) in the second to third week. (3) In the 12th–13th-day foetus, 60–70% of cholesterol is of maternal origin. Subsequently this value decreases so that in the last days of foetal life 80–85% of the cholesterol is of synthetic origin. (3) It would appear that the source of foetal exchangeable cholesterol of synthetic origin is the placenta. (5) After birth, the milk provides about two-thirds of the exchangeable cholesterol during the first 2 weeks, but after the 3 weeks nearly 80% of exchageable cholesterol is of synthetic origin. (6) Transformation into bile acids would seem to develop simultaneously with the secretion of synthesised cholesterol. (7) The fractional rate of turn-over of exchangeable cholesterol attains its highest value (8% per day) at the 4th week. (8) 80% of the milk cholesterol originates by excretion from the plasma.

The incorporation of ¹⁴C-labelled acetate into fatty acids by macrophages in vitro was investigated by gas phase chromatography. 37.3% of the ¹⁴C-labelled acetate was incorporated into palmitic acid, 18.4% into oleic acid and smaller amounts into myristic, stearic and linoleic acid. The specific activity of myristic acid was high relative to palmitic acid, but that stearic and oleic acid similar to that of palmitic. Linoleic acid was only labelled at low specific activity. The inter-relationship of the synthesis of different fatty acids in the metabolism of macrophages is discussed.