De novo CDP-choline-dependent glycerophosphorylcholine synthesis and its involvement as an intermediate in phosphatidylcholine synthesis

The activity of CDP-choline-dependent glycerophosphorylcholine synthetase (CDP-choline:sn-3-glycerophosphate cholinetransferase), a newly discovered enzyme involved in the recently proposed pathways of acyl-specific phosphatidylcholine synthesis, is reported in rat liver. Endogenous CDP-choline, synthesized via the CMP-driven back reaction of phosphorylcholine transferase, is also shown to be a choline donor for this glycerophosphorylcholine synthetase. The function of glycerophosphorylcholine as an intermediate in phosphatidylcholine synthesis is demonstrated by specific isotope trapping whereby unlabelled glycerophosphorylcholine inhibited label incorporation from sn-[14C]glycerol-3-phosphate into phosphatidylcholine in mouse gastrocnemius, a tissue that is essentially devoid of the cytidine pathway for phosphatidylcholine synthesis and uses a non-allelic glycerophosphorylcholine synthetase (exogenous PC:sn-3-glycerophosphate cholinetransferase) in the synthesis of glycerophosphorylcholine.

The hydrolysis of glycerophosphocholine by rat brain microsomes: activation and inhibition

Experiments with glycerophosphocholine phosphodiesterase (GPC diesterase, EC 3.1.4.2.) in rat brain microsomes suggest that, although its activity is inhibited by low concentrations of calmidazolium, its dependence on Ca2+ ions is not modulated by calmodulin. The activity of glycerophosphocholine choline phosphodiesterase (choline phosphohydrolase, EC 3.1.4.38) was much lower than that of the GPC diesterase. A relatively inexpensive method for the preparation of sn-glycero-3-phospho [Me-14C]choline is described.

Free radicals: a potential pathogenic mechanism in inherited muscular dystrophy

Despite years of intensive work, the biochemical defect responsible for the pathogenesis of inherited muscular dystrophy has not been identified either in humans or animal models. This review examines evidence in support of the hypothesis that free radicals may be responsible for muscle degeneration in this disorder. A variety of cellular abnormalities noted in dystrophic muscles can be accounted for by free radical mediated damage. In addition, chemical by-products associated with free radical damage are found in dystrophic muscle tissue from humans and animals with this disease. Various enzymatic antioxidant systems can be enhanced as a normal cellular response to oxidative stress, and such changes are seen both in dystrophic muscle cells and certain other tissues of dystrophic animals. An increased level of free radical damage would follow from either: enhanced production of free radical species, or a deficient component of the cellular antioxidant system, such as vitamin E. The free radical hypothesis of muscular dystrophy can account for data supporting several alternative theories of the pathogenesis of this disease, as well as other observations which have not previously been explained.

31P-NMR studies of the metabolisms of the parasitic helminths Ascaris suum and Fasciola hepatica

31P-NMR has been applied to the study of the metabolisms of the intact parasitic helminths Ascaris suum (the intestinal roundworm) and Fasciola hepatica (the liver fluke). After calibration of the chemical shift of Pi in muscle extracts the internal pH of adult Ascaris worms and the effect of the pH of the external medium on the organism's internal pH were measured. Assignments of nearly all of the observable 31P resonances could be made. A large resonance from glycerophosphorylcholine whose function is unclear was observed but no signals from energy storage compounds such as creatine phosphate were detected. The profiles of the phosphorus-containing metabolites in both organisms were monitored as a function of time. Changes in sugar phosphate distributions but not ATP/ADP were observed. Studies of the drug closantel on Fasciola hepatica were performed. Initial effects of the drug were a decrease in glucose 6-phosphate and an increase in Pi with no substantial change in ATP levels as observed by 31P-NMR. Studies involving treatment with closantel followed by rapid freezing, extraction, and analytical determination of glycolytic intermediates confirmed NMR observations. This NMR method can serve as a simple noninvasive procedure to study parasite metabolism and drug effects on metabolism.

Acylation of 1-alkenyl-glycerophosphocholine and 1-acyl-glycerophosphocholine in guinea pig heart

The deacylation-reacylation process has been shown to be an important pathway for phospholipids to attain the desired acyl groups at the C-2 position. The acylation of 1-acyl-glycerophosphocholine (-GPC) in mammalian hearts has been well documented, but the acylation of 1-alkenyl-GPC has not been described. In this paper, we demonstrate the presence of acyl-CoA: 1-alkenyl-GPC acyltransferase for the acylation of 1-alkenyl-GPC in mammalian hearts; the highest activity is found in guinea pig heart. The guinea pig heart 1-alkenyl-GPC acyltransferase has only 10-40% of the 1-acyl-GPC acyltransferase activity, and both activities are located in the microsomal fraction. However, these two enzymes respond differently to cations, detergents and heat treatment, and the two enzymes also display different acyl specificity. Kinetic studies indicate that both reactions could not be accommodated by the same catalytic site. The results provide strong evidence that the two activities are from separate and distinct proteins. The specificity of 1-alkenyl-GPC acyltransferase for unsaturated species of acyl-CoA may play an important role in the maintenance of the high degree of unsaturated acyl groups found in guinea pig heart plasmalogens.

Phosphorus-31 nuclear magnetic resonance study of post mortem catabolism and intracellular pH in intact excised rabbit muscle

Phosphorus-31 nuclear magnetic resonance has been used to study the post mortem catabolism of high-energy phosphate compounds and the associated intracellular pH variation in pure fast- and slow-twitch rabbit muscles and in rabbit muscle with mixed fiber types. Comparative results from pure fiber types are reported for the first time. Large amounts of glycerophosphorylcholine (14.1 mumol/g fresh tissue) are found in the internal conoidal bundle (ICB), a pure oxidative slow twitch muscle, whereas the m. psoas major (PM), a pure glycolytic fast twitch muscle and the m. gastrocnemius caput medialis (GCM), with mixed fiber types, are devoid of the same metabolite. The total content of phosphorylated metabolites is constant among the three muscle types. The time-dependent post mortem changes in phosphorylated metabolites display the expected rapid drop in phosphocreatine and a simultaneous increase in intracellular inorganic phosphate. However, the ATP level remains constant during more than 2 h. Rate constants for metabolite breakdown and apparent ATPase activity have been determined. The comparative kinetics of intracellular acidosis at 25 degrees C yield rates of 3.3 X 10(-3) pH unit/min for PM, 2.7 X 10(-3) pH unit/min for GCM and 3.0 X 10(-3) pH unit/min for ICB. Initial intracellular pH values are 7.07, 7.20 and 7.02, respectively. Upon aging, the heterogeneity of the Pi signal reflects the existence of cellular compartments with different internal pH. The results suggest that the more intense low-pH Pi signal arises from the sarcoplasmic reticulum while the less intense resonance would reflect the sarcoplasmic higher pH. The temperature effect on post mortem catabolism in the 15-25 degrees C range has been documented. As expected, phosphocreatine and ATP breakdown increase with temperature but at a higher rate for slow-twitch ICB than for fast-twitch PM.

Glycerylphosphorylcholine in selected forms of male infertility

GPC was studied in the seminal plasma of 35 normozoospermic men, 34 cases of azoospermia due to bilateral deferent obstruction, 34 cases of azoospermia due to bilateral ejaculatory duct obstruction, 10 vasectomized patients, 6 vasectomized patients after vasovasostomy and 118 cases of spermatogenetic arrest without obstruction of the seminal ducts. Values of GPC in azoospermia due to deferent or ejaculatory ducts obstruction and to vasectomy are significantly lower than in normozoospermic subjects (p less than 0.001). Levels of GPC increased (p less than 0.05) following vasovasostomy. Although GPC values in secretory azoospermia were higher than those in cases of duct obstruction, they were still lower than in normozoospermic (p less than 0.001). The most likely source of GPC is the epididymis. These results support the assumption that GPC originates mainly in the epididymis. The absence of germinal cells in the epididymis could explain the decreased levels of GPC in azoospermia due to arrest of spermatogenesis.

In vivo 31P-MR spectroscopy of the liver in the infant rabbit to study the effect of hypoxia on the phosphorus metabolites and intracellular pH

In vivo 31P-magnetic resonance spectroscopy (MRS) with a chronically implanted detection coil was used to study the effect of hypoxia on the phosphorus metabolites and intracellular pH in the liver of infant rabbits. A two-turn 10-mm radiofrequency coil was placed between the hepatic lobes in each of four infant New Zealand white rabbits (10-16 days old). Two days later, the rabbits were anesthetized and mechanically ventilated with 1.5% isoflurane in 98.5% O2. Blood gases, heart rate, and mean arterial pressure were monitored. 31P-MR spectra were continuously obtained every 5 minutes during 15 minutes of hyperoxia (PaO2 greater than 250 torr), 15 minutes normoxia (PaO2 approximately equal to 100 torr), 60 minutes hypoxia (PaO2 = 24 torr +/- 4 S.D.), and 15 minutes recovery (hyperoxia). In addition, 31P-MR spectra of perchloric-acid extracts of the liver of an adult and of an infant rabbit, removed under normoxic conditions, were examined. The 31P-MR spectra of liver of the normoxic adult (in vitro) and infant rabbits (in vitro and in vivo) revealed a high level of phosphodiesters, namely glycerol-3-phosphorylethanolamine, glycerol-3-phosphorylcholine, and phosphoenolpyruvate, compared with that reported for adult rat and adult mouse liver. The inorganic phosphate (Pi)-to-adenosine triphosphate (ATP) ratio was about 0.90 during hyperoxia and during normoxia. Within 15 minutes after induction of hypoxia, the level of phosphorus metabolites changed markedly: The ATP decreased 41% +/- 18 S.D. (P less than .01) and the Pi increased 206% +/- 29 S.D. (P less than .01); the Pi/ATP ratio was 5.0.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the acylation of 1-acyl-sn-glycero-3-phosphoinositol and 1-acyl-sn-glycero-3-phosphocholine in neuronal nuclei in vitro using radioactive arachidonate and oleate

A neuronal nuclear fraction (N1) was isolated from cerebral cortices of 15-day-old rabbits. Samples of N1 were incubated with a radioactive fatty acid ([3H]arachidonate or [14C]oleate), acylation cofactors, and 1-acyl-sn-glycero-3-phosphoinositol (1-acyl-GPI) or 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC). In competition studies, both radioactive fatty acids were incubated with one lysophospholipid or the two lysophospholipids were incubated with one radioactive fatty acid. Using [3H] arachidonate and one lysophosphoglyceride, a maximal rate of incorporation into phosphatidylinositol (PI) was found at a relatively low concentration of 1-acyl-GPI (10 microM), while increasing rates of incorporation into phosphatidylcholine (PC) were seen with increasing concentrations of 1-acyl-GPC (to 65 microM). At low concentrations of lysophosphoglyceride (less than or equal to 25 microM) the rate of arachidonate incorporation into PI greatly exceeded rates of arachidonate incorporation into PC. This higher rate of arachidonate incorporation into PI was also seen in incubations where both lysophospholipids were present. For oleate, greater rates of incorporation into PC were found in comparison with rates of labelling of PI in assays using relatively high concentrations of one or both lysophospholipids. When comparing arachidonate and oleate, in assays with one or both fatty acids, the polyunsaturate showed at least threefold higher rates of incorporation into PI. For PC labelling higher rates of arachidonate incorporation were evident at the higher concentrations of 1-acyl-GPC and the superiority over oleate was not as marked as that seen in PI labelling.

Heterogeneity in the metabolism of the arachidonoyl molecular species of glycerophospholipids of rabbit alveolar macrophages. The interrelationship between metabolic activities and chemical structures of the arachidonoyl molecular species

The relative incorporation of [3H]arachidonic acid (20:4) into individual molecular species containing 20:4 at the 2 position (18:1-20:4, 16:0-20:4 and 18:0-20:4 species) of diacyl and ether-linked glycerophosphocholine, glycerophosphoethanolamine and glycerophosphoinositol of rabbit alveolar macrophages has been measured by reversed-phase high-performance liquid chromatography (HPLC). The rate of incorporation of [3H]20:4 into the molecular species of glycerophospholipids was greatly influenced by their structures. The reversed-phase HPLC analysis allowed elucidation of the influence of structural differences, such as the nature of the polar head group, the fatty chain at the 1 position and the chemical form of the bond of the fatty chain attached at the 1 position on the uptake of [3H]20:4 by comparison of the specific radioactivities of arachidonoyl molecular species having the same structures, except that one of the three kinds of moiety was different. The specific radioactivities of the molecular species containing choline head groups were significantly higher than those containing ethanolamine and inositol moieties. The specific radioactivities of diacyl molecular species were considerably higher than those of ether-linked molecular species. The nature of the fatty chain attached at the 1 position also influenced the uptake of [3H]20:4 into glycerophospholipids. The arachidonoyl molecular species containing 18:1 at the 1 position were preferentially labelled with [3H]20:4 as compared to the corresponding 16:0-20:4 and 18:0-20:4 species either of diacyl or ether-linked glycerophospholipids. The present results suggest that the acyltransferase involved in the incorporation of 20:4 into glycerophospholipids has selectivity for the structures of glycerophospholipids and the order of selectivity of this enzyme for the arachidonoyl molecular species, deduced in the present experiments, was as follows: choline head group greater than ethanolamine and inositol groups, acyl bond greater than ether and vinyl ether bonds, 18:1 fatty chain greater than 16:0 and 18:0 fatty chains at the 1 position. Comparison of the metabolic activities of all major arachidonoyl molecular species of glycerophospholipids having a single structure is reported here for the first time.

Impaired biosynthesis of highly unsaturated phosphatidylcholines: a hypothesis on the molecular etiology of some muscular dystrophies

A brief review of the literature concerning the synthesis of phosphatidylcholine and phosphatidylethanolamine in muscle suggests that the cytidine pathways are replaced by the recently proposed acyl-specific de novo and salvage glycerolphosphodiester pathways (Infante, 1984) in fully differentiated muscle. An analysis of published data suggests an impaired synthesis of 4,7,10,13,16,19-docosahexaenoic phosphatidylcholine, at the level of de novo sn-3-glycerolphosphorylcholine synthesis, as the primary defect in Duchenne and (dy) murine muscular dystrophies. This phosphatidylcholine species is postulated to be required for optimum sarcoplasmic Ca2+ transport activity. It is proposed that this impairment initiates the secondary series of events which lead to the observed pathology of these diseases. Based on some predictions of the hypothesis, potential diagnosis and treatments are suggested.

31P-NMR studies of metabolite compartmentation in Fasciola hepatica

Fasciola hepatica, the common liver fluke, is an anaerobic parasitic worm. Possible compartmentation of metabolites between different cell types, metabolic compartments, and free and macromolecule-bound species was investigated using 31P-NMR. A spectrum of the intact worm shows unusual metabolic features, among which are large amounts of glycerolphosphorylcholine, phospholipids mobile on the NMR time-scale, and free cytosolic ADP. Spectra from cells as different as those in oral sucker tissue and eggs showed similar features. Acidosis after serotonin administration was associated with parallel changes in chemical shifts of intracellular Pi and glucose 6-phosphate, suggesting that they are in the same metabolic compartment. Although 13.4 +/- 1.1 mumol/g wet wt. (n = 3) Mg2+ is present in fluke tissue, a considerable fraction is sequestered out of the cytosol. The intracellular free [Mg2+] was independently estimated from the chemical shifts of ATP and ADP as 1.6 +/- 0.5 mM and 2.9 +/- 0.7 mM, respectively. Quantitation of observable phosphate-containing metabolites in whole tissue and in perchlorate extracts demonstrated that 60% of the total ADP and 50% of the total Pi are 'NMR-invisible' in the intact fluke and therefore probably bound to macromolecules in the cells. The apparent ATP/ADP X Pi free concentration ratio is much lower in this anaerobic tissue than in mammalian oxidative tissues.

Modulations of glycerophosphorylcholine and phosphorylcholine in Friend erythroleukemia cells upon in vitro-induced erythroid differentiation: a 31P NMR study

A 31P NMR study has been carried out on Friend erythroleukemia cells (FLC) induced to undergo erythroid differentiation in vitro. Significant levels of glycerophosphorylcholine (GroPCho) and phosphorylcholine (P-Cho) were identified both in the untreated cells and in their PCA extracts. In FLC treated 4 days in vitro with either dimethylsulfoxide (DMSO) or hexamethylenebisacetamide (HMBA), the intracellular concentration of P-Cho was markedly increased, whereas that of GroPCho appeared to be significantly reduced. HMBA was more effective than DMSO in producing this effect. The concomitant modulations of GroPCho and P-Cho in differentiated FLC suggest the hypothesis that erythroid differentiation involves modifications of the regulatory mechanisms controlling biosynthesis and catabolism of phospholipids.

Selective increase in acylation of 1-acylglycerophosphorylcholine in livers of rats and mice by peroxisome proliferators

Rats were fed a diet containing p-chlorophenoxyisobutyric acid (clofibric acid). Activity of microsomal 1-acylglycerophosphorylcholine (1-acyl-GPC) acyltransferase in liver was increased approx. 3-fold by the treatment with clofibric acid. The treatment of rats with clofibric acid did not increase activity of microsomal 2-acyl-GPC acyltransferase. Feeding a diet containing 2,2'-(decamethylenedithio)diethanol (tiadenol), di(2-ethylhexyl)phthalate or acetylsalicylic acid also resulted in a selective increase in the activity of 1-acyl-GPC acyltransferase in rat liver. Treatment with clofibric acid increased the activity of 1-acyl-GPC acyltransferase in liver of mouse as well as rat, but did not change the activity in liver of guinea-pig. The relative rate of acylation of 1-acyl-GPC with various acyl-CoAs by hepatic microsomes was not changed by the treatment of rats with clofibric acid.

A hypothesis: noncyclic phosphodiesters may play a role in membrane control

The study of the metabolism of GPC and SEP has the potential to demonstrate a previously undiscovered method by which the cytosol can communicate with membrane.

Uptake and output of various forms of choline by organs of the conscious chronically catheterized sheep

The net uptake and output of plasma unesterified choline, glycerophosphocholine, phosphocholine and lipid choline by organs of the conscious chronically catheterized sheep were measured. There was significant production of plasma unesterified choline by the upper- and lower-body regions and the alimentary tract and uptake by the liver, lungs and kidneys. The upper- and lower-body regions drained by the venae cavae provided the bulk (about 82%) of the total body venous return of plasma unesterified choline. Production of plasma unesterified choline by the alimentary tract was approximately balanced by the plasma unesterified choline taken up by the liver, and was almost equal to the amount of choline secreted in the bile. There was a considerable amount of glycerophosphocholine in the liver and there was production of plasma glycerophosphocholine by the liver and uptake by the lungs and kidneys. Glycerophosphocholine was higher in the plasma of sheep than in that of rats. Plasma phosphocholine was produced by the alimentary tract and kidneys. There was production of plasma lipid choline by the upper- and lower-body regions drained by the venae cavae. The results suggest that the sheep synthesizes substantial amounts of choline in ectrahepatic tissues and has the capacity for extensive retention and recycling of bile choline. These observations, coupled with a slow turnover of the endogenous choline body pool, explain the low requirement of sheep for dietary choline in contrast with non-ruminant species.

Mobilization of arachidonic acid between diacyl and ether phospholipids in rabbit alveolar macrophages

The metabolism of 20:4 (arachidonic acid) in alkenylacyl, alkylacyl and diacyl lipid classes in choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP) in rabbit alveolar macrophages was examined. [3H]20:4 was very rapidly incorporated into diacyl glycerophosphocholine (GPC). After the removal of free 20:4, the radioactivity was gradually lost from diacyl GPC. Concomitantly, the radioactivities in alkylacyl GPC and alkenylacyl glycerophosphoethanolamine (GPE) were increased, indicating that 20:4 was mobilized from diacyl GPC to alkylacyl GPC and alkenylacyl GPE. The mobilization was considered to be a 20:4-specific event. The gradual accumulation of 20:4 in ether phospholipids leads to a high abundance of 20:4 in these lipids. These results suggest metabolic relationships between 20:4 and ether phospholipids, including platelet-activating factor (PAF).

Uptake and metabolism of polyene phosphatidylcholine in rat brain

The rate and mechanism of incorporation of polyene phosphatidylcholine (PPC) and lysophosphatidylcholine into rat brain have been studied with double labelled substrates administered intravenously. It was found that both substances could be taken up into the brain with transfer velocities of the order: lysophosphatidylcholine much greater than phosphatidylcholine greater than glycerophosphocholine. Similarities between the 3H/14C ratios of the substrates and the brain phosphatidylcholine, together with retention of the label in the original acyl moieties, as demonstrated by phospholipase A2 hydrolysis, gave conclusive proof that both PPC and lysophosphatidylcholine are taken up intact into the brain.

Effect of flutamide, a nonsteroidal antiandrogen on functional maturation of the epididymis of rat

The effect of flutamide, a non-steroidal antiandrogen on the growth and secretory function of the epididymis of rat during transition from prepubertal age (35 days old) to puberty (50 days old) was investigated. The results showed that the antiandrogen interfered with the growth of all the genital organs accompanied by a marked reduction in the secretory function of the epididymis as revealed by lowered levels of sialic acid and glycerylphosphorylcholine. These findings are discussed in relation to our previous observations in adult rats.

Generation of phosphodiesters during fast-to-slow muscle transformation. A 31P-NMR study

During rabbit fast-to-slow twitch muscle transformation, in response to electrical stimulation, the compound glycerophosphocholine can be detected in these muscles by 31P-NMR. This compound is not detectable in contralateral control muscles but is present in slow twitch soleus.

Flutamide as an androgen antagonist on epididymal function in the rat

The purpose of this study was to investigate whether flutamide (alpha-alpha-alpha--Trifluro-2-methyl-4'-nitro-m-propionatoluidide), a nonsteroidal compound acts as an androgen antagonist at the level of the epididymis. For comparison, cyproterone acetate was also evaluated under identical experimental conditions. The levels of glycerylphosphorylcholine (GPC), sialic acid, total phospholipids were used as functional indices of epididymis and, in addition, weights of the accessory sex organs were recorded. Adult male rats castrated and maintained on testosterone therapy (TP: 250 microgram/rat: i.m.) were treated with flutamide (25 mg/kg, oral) or cyproterone acetate (25 mg/kg, s.c.). Castration caused a reduction in the weight and secretory activity of the epididymis which was restored to near normal following TP replacement therapy. GPC level was found to be the most sensitive index of epididymal secretory function. The two antiandorgens antagonised the action of TP on all the accessory sex organs. These findings are discussed in relation to our previous study which demonstrated the lack of effect of flutamide on the epididymal function of intact rats.

The acylation of 1-acyl-sn-glycero-3-phosphorylcholine by glial and neuronal nuclei and derived neuronal nuclear envelopes: a comparison of nuclear and microsomal membranes

A neuronal nuclear fraction (N1), a glial nuclear fraction (N2) and a fraction containing microsomal membranes (P3) were isolated from homogenates of cerebral cortices of 15-day-old rabbits. A nuclear envelope fraction (E) was prepared from fraction N1. In comparison with the parent fraction N1, fraction E had a much lower yield of protein (0.077 mg/g cerebral cortex), a low specific DNA content, an eightfold higher specific phospholipid content (0.85 mumol phospholipid phosphate/mg protein) and a very similar phospholipid distribution profile. Using 100, 50, and 25 microM 1-acyl-sn-glycero-3-phosphorylcholine (labelled with [3H]palmitate) and 100 microM oleoyl CoA, the activity of acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase was studied in vitro. Fractions N1 and N2 had specific activities which were two to three times the specific activities shown for fraction P3. Fraction E was particularly enriched in this acylation activity and had specific activities which were 6 times those of fraction N1 and 11-19 times those of fraction P3. The existence of nuclear acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase activity was indicated as was a particularly high concentration of this enzyme within the nuclear envelope. In assays of lysolecithin-lysolecithin transacylase activities, fraction N2 (glial nuclei) showed the highest specific activities, being three to four times those of fractions N1 or P3. This transacylase activity (N2) was as high as 40% of the corresponding acyltransferase activity measured in this fraction using oleoyl CoA as acyl donor.

Phospholipid metabolism of dog liver under hypoxic conditions induced by ligation of the hepatic artery

Ischemic hypoxic liver was induced in dogs by ligation of the hepatic artery. About 67% of the dogs died of liver necrosis within 1 or 2 days (severe cases), and the rest survived (mild cases). In the severe cases, the decreases in the contents of total lipids, phospholipids and proteins of the liver after 24 h were 24, 46 and 12%, respectively, of the original values. The marked decrease in phospholipids was due to decreases in the microsomal and mitochondrial fractions. In the mild cases, similar but smaller decreases occurred and decrease of phospholipids occurred only in the microsomal fraction. The main phospholipids were choline and ethanolamine glycerophospholipids, and their molecular species were analyzed. In the severe cases, ligation resulted in relative increases in mono- and diene species and a decrease in polyene species. No increase in phospholipase activity was found at various times after ligation of the hepatic artery. Penicillin-treated dogs all survived and showed little decrease in liver phospholipids.

The suitability of different acyl acceptors as substrates for the acyl-Coa : 2-acyl-sn-glycero-3-phosphorylcholine acyltransferase in rat liver microsomes

The fatty acid selectivity of the acyl-CoA : 2-acyl-sn-glycero-3-phosphorylcholine acyltransferase towards different acyl acceptors was studied in rat liver microsomes. The individual molecular species of 2-acylglycerylphosphorylcholine tested as enzyme substrates contained either palmitate, stearate, oleate, linoleate, linolenate or arachidonate with an equimolar mixture of [14C]palmitoyl-CoA plus [3H]stearoyl-CoA serving as the acyl donor. At 2-acyl-sn-glycero-3-phosphorylcholine concentrations of 16 or 64 microM, the various acyl acceptors gave generally similar reactivities, although reaction velocities with the linoleoyl, linolenoyl or arachidonoyl species were moderately greater than those with 2-stearoyl-sn-glycero-3-phosphorylcholine. Regardless of the acyl acceptor tested, little preference towards either palmitoyl-CoA or stearoyl-CoA was indicated at 64 microM 2-acyl-sn-glycero-3-phosphorylcholine whereas a distinct preference for stearate over palmitate (by 1.9--2.6-fold) was exhibited when a lower concentration (16 microM) of the acceptor was employed. The results support the potential importance of the acyl-CoA : 2-acyl-sn-glycero-3-phosphorylcholine acyltransferase for the synthesis of 1-stearoyl 2-unsaturated species of phosphatidylcholine. However, it cannot independently account for the varying palmitate : stearate ratios in the 1-position of this phospholipid when different unsaturated fatty acids reside in the 2-position.

Interaction of dilauroylglycerophosphocholine with erythrocytes: pre-hemolytic events and hemolysis

The process of interaction of dilauroylglycerophosphocholine with erythrocytes that eventually results in hemolysis was examined. 1. The rate of uptake of dilauroylglycerophosphocholine by human erythrocytes was rather slow, but increased with increasing temperature. 2. The first observable change of human erythrocytes induced by dilauroylglycerophosphocholine was a morphological change from discocytes to spheroechinocytes. This change preceded K+ leakage. 3. Adsorption of dilauroylglycerophosphocholine to human erythrocytes caused K+ leakage. The rate of K+ leakage was also temperature-dependent. The temperature-dependence was due to the temperature-dependence of lipid uptake, because in order to cause K+ leakage a given amount of dilauroylglycerophosphocholine must be bound to the erythrocytes, irrespective of the temperature. 4. The temperature-dependence of hemolysis of human erythrocytes was different from that of pre-hemolytic events (morphological change, adsorption of lipids and K+ leakage). Hemolysis was rapid below 10 and above 37 degrees C, but slow at about 25 degrees C. The hemolysis observed below 10 degrees C seemed to be a 'colloid osmotic lysis', since it occurred immediately after K+ leakage, but the hemolysis above 37 degrees C may not be a colloid osmotic lysis. Above 37 degrees C, additional binding of dilauroylglycerophosphocholine to the erythrocyte membrane may cause hemolysis by a different mechanism from that working below 10 degrees C. 5. Above 25 degrees C, most human erythrocytes are resistant to colloid osmotic lysis induced by dilauroylglycerophosphocholine. It can be concluded that human erythrocytes are composed of two types of population, one resistant, and one sensitive to colloid osmotic lysis. The mechanism of the resistance was sensitive to temperature, pH and various sulfhydryl agents. 6. Pig erythrocytes were hemolysed immediately after K+ leakage even above 25 degrees C, indicating that they were sensitive to a colloid osmotic mechanism over the whole temperature range tested. Pig erythrocytes may lack the 'mechanism' giving resistance to colloid osmotic lysis. The process of hemolysis of erythrocytes by dilauroylglycerophosphocholine is shown schematically.

Changes in the content and acyl group composition of glycerophospholipids of brain endothelial cells of the developing rat

The glycerophospholipid (GPL) content and acyl group compositions of isolated brain endothelial fractions have been determined in the developing rat. During development there is a marked change in the proportions of ethanolamine glycerophospholipids (EGP) to choline glycerophospholipids (CGP), the former rising while CGP falls with age. The acyl group compositions of plasmenylethanolamine (P-GPE) and 1,2-diacyl-sn-glycero-3-phosphocholine (D-GPC) after significantly during development; both show a decline in saturated fatty acids (SFAs) and a rise in the n-6/SFA ratio, in contrast to a constancy in composition of 1,2-diacyl-sn-glycero-3-phosphoethanolamine (D-GPE). The degree of change in the acyl group composition in a particular GPL fraction is related to the rate of its accumulation and to the proportional increase in concentration, fractions accumulating most rapidly or increasing markedly in concentration showing the greatest acyl group compositional change. The possible significance of the high proportion of SFAs in P-GPE and D-GPC fractions in the developing brain endothelial fraction is discussed in relation to the altering blood-brain barrier capacities observed with age.

Glycerol vic-cyclic phosphate in rat tissues

On labelling rat tissues with 32P, a radioactive phosphate ester can be isolated with the same chromatographic and ionophoretic properties and susceptibility towards a specific phosphodiesterase and acid as glycerol vic-cyclic phosphate. By comparison with precursor phosphoglycero-derivatives in the same tissues it is calculated that the concentration in liver, kidney and brain is in the order of 0.7--4.0 nmol/g wet wt.

Origin of glycerylphosphorylcholine, inositol, N-acetylaminosugar, and prostaglandins in human seminal plasma and their effects on sperm metabolism

The origin of glycerylphosphorylcholine (GPC), N-acetylaminosugar, inositol, and prostaglandins in human seminal plasma was investigated by correlating the concentration of these components in split ejaculates with known marker constituents. Fructose and acid phosphatase were selected as markers of the secretory activity of the seminal vesicles and prostate gland, respectively, and spermatozoa indicated epididymal origin. The concentration of fructose was lowest in the first fraction of the semen and increased to a maximum in the final portion. Prostaglandins E and F and N-acetylaminosugar values closely followed this pattern, indicating that these components originate in the seminal vesicles. The concentration of spermatozoa was high in the first two fractions, decreasing to a minimum in the final fraction. The distribution of GPC was similar to that of the spermatozoa, indicating that the epididymis secretes this compound. Inositol levels were similar in all fractions, indicating that it is probably present in epididymal, vesicular, and prostatic fluid. Human spermatozoa were unable to utilize N-acetylglucosamine or inositol. High concentrations of some prostaglandins (100 micrograms/ml of PGF1 alpha, 15S 15 met. F2 alpha, PGA1, and PGA2) depressed the endogenous oxygen uptake of human spermatozoa.

Substrate specificity of enzymes catalyzing the biosynthesis of ionic alkoxylipids from alcohols

An equimolar mixture of homologous saturated alcohols (13:0, 15:0, 17:0, 19:0) and an equimolar mixture of vinylogous alcohols (19:0, 19:1, 19:2) were fed to two groups of rats. All of the odd-numbered alcohols were incorporated into the ionic alkoxylipids of the rats' small intestine. Pronounced quantitative differences in the distribution of the various odd-numbered alkyl and alk-1-enyl moieties of choline phosphoglycerides and ethanolamine phosphoglycerides gave evidence to differences in the specificity of the enzyme system catalyzing the biosynthesis of alkoxylipids from long-chain alcohols.

[Influence of testicular fluid, spermatozoa and androgens on physiological activity of rat epididymis]

By ligation of the efferent duct and the corpus epididymis, the GPC concentration in this delimited anterior region decreased. However, HCG infection increased the GPC concentration. When spermatozoa are present in the epididymal tubule there is always a decrease in GPC concentration in these experimental conditions. Activity of the epididymis is disturbed by ligation.

Regulation of phospholipase A2 activity by different lipid-water interfaces

The activity of pancreatic phospholipase A2 (EC 3.1.1.4) is controlled not only by the architecture of the catalytic site, but is also strongly dependent on the penetrating power of the interface recognition site and the packing density of the lipid-water interface. The influence of the latter two factors on the interface activity has been investigated using chemically modified phospholipases A2 in which the NH2-terminal L-Ala8 has been replaced by DL-[3-13C]Ala, or in which the polypeptide chain has been elongated with DL-[3-13C]Ala. The [DL-(3-13C)Ala8]phospholipase A2 could be resolved into the pure diastereoisomers, [D-(3-13C)Ala8]phospholipase A2 and [L-(3-13C)Ala8]phospholipase A2 by elution on Sephadex G-100 in the presence of a micellar lipid-water interface, as well as by conventional ion exchange chromatography on carboxymethylcellulose. Similar procedures did not effect, however, a separation of DL-[3-13C]Ala7-phospholipase A2 into their respective diasteroisomers, indicating the strategic role of the NH2-terminal L-Ala8 residue in the interaction process between the enzyme and lipid-water interfaces. Kinetic experiments using various micellar short chain lecithins revealed the apparent absence of an interface recognition site in [D-(3-13C)Ala8]- and DL-[3-13C]Ala7-phospholipase A2, while these proteins still possess considerable enzymatic activity toward monomeric substrates. In contrast, however, kinetic experiments using monomolecular surface films, allowing a continuous change in surface density of the substrate molecules, revealed that [D-(3-13C)Ala8]- and DL-[3-13C]Ala7-phospholipase A2 at low surface pressure possess about 60 and 30% of the interface activity of native phospholipase A2, respectively. These results therefore suggest that the modified phospholipases A2 do possess an interface recognition site although less powerful as compared to that of the native enzyme, enabling the estimation of the surface density of micellar short chain lecithins.

The effect of chronic ethanol administration on arachidonyl transfer to 1-acyl-glycerophosphorylcholine in rat brain synaptosomal fraction

Enzymatic transfer of arachidonate to synaptosomal diacyl-GPC in a group of rats (n=14) administered 30% ethanol by intragastric intubation for 21 days was 24% higher than controls (n=5) (P less than 0.05). No apparent difference in enzymic activity was observed with respect to different periods of withdrawal (8-24 hrs). The acyl transferase activity in another group of rats (n=5) which were given 15% ethanol as the sole drinking source for 13 months was 58% higher than controls (P less than 0.025). The increase in acyl transferase activity with respect to the two types of chronic ethanol administration may be due to an adaptive mechanism in brain to facilitate the increase in membrane transport activities which are known to occur under the influence of ethanol.

Enzymic formation of Glycerol 1:2-cyclic phosphate

Glycerol 1:2-cyclic phosphate is released simultaneously with glycerophosphate when kidney glycerophosphinicocholine diesterase (EC 3.1.4.2) acts on glycerylphosphorylcholine and glycerylphosphorylethanolamine. The percentage of cyclic phosphate ester formed is increased at pH values below the optimum and is decreased when Mg2+ or Ca2+ is added to stimulate the reaction.