N-Acylation of dog heart ethanolamine phospholipids by transacylase activity

A comparison of three methods of soft ionization mass spectrometry of crude phospholipid extracts

Many different classes of phospholipids were identified from crude extracts of hearts by three soft ionization mass spectrometric techniques: liquid matrix secondary ion mass spectrometry in the negative mode, (-)LSIMS, and in the positive mode, (+)LSIMS, and field desorption. (-)LSIMS and (+)LSIMS are complementary methods. In some cases it was possible to establish the fatty acid and aldehyde composition and position of some phospholipid classes, by the analysis of fragments.

Occurrence of N-acylethanolamine phospholipids in fish brain and spinal cord

N-Acylethanolamine phospholipids were identified in the central nervous system of the fresh water fish, pike (Esox lucius) and carp (Cyprinus carpio), at levels ranging from 0.1 to 0.9% of total phospholipid. The N-acylethanolamine phospholipids of carp brain were isolated and characterized by chemical, biochemical and spectroscopic methods. Two major species, 1,2-diacyl-sn-glycero-3-phospho(N-acyl)ethanolamines (approx. 30%) and 1-O-(1'-alkenyl)-2-acyl-sn-glycero-3-phospho(N-acyl)ethanolamines (approx. 70%) were identified. The N-acyl groups of each species consisted primarily of 16:0 (approx. 60%) but also contained 16:1, 18:0 and 18:1 (approx. 10% each) and a number of trace constituents. The N-acylethanolamine phospholipids had O-acyl and O-alkenyl group compositions similar but not identical to those of the ethanolamine phospholipids of the same tissue. N-Acylethanolamine phospholipids were present in all subcellular fractions of carp brain, except mitochondria.

Properties of canine myocardial phosphatidylethanolamine N-acyltransferase

Dog heart contains a membrane bound N-acyltransferase (transacylase) which transfers acyl groups from the sn-1 position of membrane phospholipids to the amino group of ethanolamine phospholipids in the presence of millimolar Ca2+ concentrations. Using crude membrane preparations, we found this N-acyltransferase activity to be heat sensitive and inhibited by sulfhydryl reagents. Pretreatment of a membrane fraction with trypsin reduced N-acyltransferase activity to 60% while pretreatment with trypsin and Triton X-100 together reduced it to 30% of the control value. At pH 8.0 both Sr2+ and Mn2+ could fully substitute for Ca2+ with respect to optimum ion concentration and molecular species of the product formed in dog heart membranes from endogenous substrates. Ba2+ was equally effective in achieving N-acylation of ethanolamine phospholipids while other divalent cations were less effective or ineffective. The reaction exhibited a pH optimum of 8.5 to 9.0 with both Ca2+ and Sr2+ while Mn2+ precipitated above pH 8.0 resulting in decreased N-acylation activity. Both phosphatidylcholine and 1-acyl lysophosphatidylcholine could serve as acyl donors. Triton X-100 at a concentration of 0.1% stimulated acyl transfer from exogenous phosphatidylcholine but inhibited acyl transfer from lysophosphatidylcholine.

Catabolism of N-acylethanolamine phospholipids by dog brain preparations

N- Acylphosphatidylethanolamine , incubated with dog brain homogenate or microsomes, was hydrolyzed to phosphatidic acid and N-acylethanolamine by a phosphodiesterase of the phospholipase D type. In the absence of F-, phosphatidic acid was further hydrolyzed to diacylglycerol and Pi while N-acylethanolamine was hydrolyzed by an amidase to fatty acid and ethanolamine. The phosphodiesterase showed an alkaline pH optimum and was also active towards N- acetylphosphatidylethanolamine , N-acyl-lysophosphatidylethanolamine, and glycerophospho (N-acyl)ethanolamine but showed little activity toward phosphatidylethanolamine and phosphatidylcholine. Ca2+ stimulated slightly at low concentrations but inhibited at higher concentrations. Triton X-100 stimulated the hydrolysis of N- acylphosphatidylethanolamine , inhibited that of N-acyl-lysophosphatidylethanolamine and glycerophospho (N-acyl)ethanolamine, and had no effect on phosphatidylethanolamine or phosphatidylcholine hydrolysis. The N-acylethanolamine hydrolase (amidase) was also present in the microsomal fraction and exhibited a pH optimum of 10.0. In addition to hydrolysis by the phosphodiesterase, N- acylphosphatidylethanolamine was also catabolized by microsomal phospholipases A1 and/or A2 to N-acyl-lysophosphatidylethanolamine, some of which was further hydrolyzed to glycerophospho (N-acyl)ethanolamine.

Biosynthesis of N-acylethanolamine phospholipids by dog brain preparations

Dog brain homogenates and subcellular preparations incubated in the presence of Ca2+ produced a new phospholipid that was isolated and identified by its infrared spectrum and by chemical degradation as a mixture of 1,2-diacyl, alkenylacyl, and alkylacyl sn-glycero-3-phospho(N-acyl)ethanolamines, 50, 45, and 5%, respectively. The N-acyl groups consisted almost exclusively of 16:0, 18:0, and 18:1 fatty acids. Formation of N-acylethanolamine phospholipids from endogenous substrates was linear for about 90 min at approximately 4.5 nmol/h/mg protein and exhibited a pH optimum of 10. Biosynthetic activity was associated with particulate fractions, primarily microsomes, synaptosomes, and mitochondria, but not with myelin. In each case, small amounts (approximately 0.5 nmol/h/mg protein) of long-chain N-acylethanolamines were also produced. Incubation of dog brain microsomes with 1,2-di[1'-14C]palmitoyl glycerophosphocholine yielded N-acylethanolamine phospholipids labeled at both N-acyl (55%) and O-acyl (45%) moieties. It appears that dog brain organelles may contain a phosphatidylethanolamine N-acyl transferase (transacylase) analogous to that recently demonstrated in the myocardial tissue.

The role of cardiolipin as an acyl donor in dog heart N-acylethanolamine phospholipid biosynthesis

N-Acylethanolamine phospholipids were produced from endogenous substrates with dog heart mitochondrial and microsomal preparations. With mitochondria the N-acyl group contained 13.8% linoleate, with microsomes only 3.6%. Cardiolipin comprised 18.5% of mitochondrial and 3.3% of microsomal lipid P and contained 93.7 and 72.4% linoleic acid, respectively. Incubation of dog heart subcellular fractions with [1-14C]linoleoyl cardiolipin in the presence of Ca2+ resulted in the formation of N-acylethanolamine phospholipids labeled primarily in the N-acyl and 1-O-acyl moieties. The data indicate that cardiolipin is the major source of linoleic acid used in the N-acylation of ethanolamine phospholipids by transacylase activity.