Substrate specificity in plasmalogen biosynthesis. Desaturation of 1-O-hexadecyloxyethyl-2-acylglycero-3-phosphoethanolamine in developing rat brain.

1-O-[1'-14C]Hexadecyloxyethyl rac-glycerol was administered to 18-day-old rats by intracerebral injection, and incorporation of radioactivity into the brain lipids was determined after 6, 24 and 48 h. Some of the substrate was catabolized by oxidative cleavage of either of the two ether bonds. Cleavage in the hexadecyloxyethyl moiety yielded labeled palmitic acid, whereas oxidative cleaveage of the glycol glycerol ether bond produced O-hexadecyl glycolic acid. The substrate was also incorporated as such into both ethanolamine and choline phospholipids. Evidence is presented for the desaturation by rat brain of 1-O-hexadecyloxyethyl-2-acyl-sn-glycero-3-phosphoethanolamine to the plasmalogen analogue, while the corresponding choline phospholipid was not desaturated.

Configurational analysis of long-chain alkanediols.

Long-chain 1,2-alkanediols can be separated into their enantiomers by thin-layer chromatography of the bis-L-acetylmandelates. The method is also applicable to the separation of enantiomeric 1,3-alkanediols. Both 2-hydroxy fatty acids and 1,2-alkanediols derived from diester waxes of rat skin have the D-configuration. The D-enantiomer of 2DL-1,2-octadecanediol is preferentially utilized by myelinating rat brain in the formation of choline phospholipids having a 1,2-octadecanediol backbone. The D-configuration of the chiral center at carbon-2 of 2-acyl-1,2-alkanediol phosphocholine corresponds to the configuration at carbon-2 of 1,2-diacyl-sn-glycero-3-phosphocholine.

Ether lipid metabolism. Incorporation of O-hexadecyl ethanediol into rat brain lipids.

1-O-[1'-14C]Hexadecyl ethanediol was administered intracerebrally to myelinating rat brain, and incorporation of radioactivity into brain lipids was followed over a 48-h period: (1) O-Hexadecyl ethanediol was metabolized primarily through oxidative ether bond cleavage, and much of the label was recovered in phospholipid acyl groups. (2) Substantial amounts of radioactivity were also found in choline and ethanolamine phospholipids having an O-hexadecyloxyethyl glycerol backbone. This means that alkyl ethanediol was used in glycerol ether biosynthesis as are long-chain primary alcohols. (3) Acidic hydrolysis of the ethanolamine glycerophosphatide fraction yielded also labeled hexadecanol which may indicate desaturation of 1-O-hexadecyloxyethyl 2-acyl glycerophosphoryl ethanolamine to the plasmalogen analogue. (4) Small amounts of the substrate were oxidized to O-hexadecyl glycolic acid and incorporated into the phospholipids. The substrate did not serve as precursor of O-hexadecyl ethanediol phosphorylcholine or phosphorylethanolamine in the brain.

Analysis and quantification of ether lipids by chromatographic methods.

Chromatographic methods, especially thin-layer chromatography (TLC) and gas-liquid chromatography (GLC) are widely used in investigations of the occurrence, molecular structure and metabolism of ether lipids. The application of such techniques to structural analysis and quantification, in combination with methods for the degradation and derivatization of ether lipids, is discussed.

Naturally occurring long-chain beta-hydroxyketones.

A fraction comprising about 0.7% of the extractable surface lipids of cabbage (Brassica oleracea) leaves was isolated and identified as a mixture of isomeric beta-hydroxyketones consisting mainly of 14-keto-16-hydroxynonacosane and 15-keto-13-hydroxynonacosane.