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B Malone

Publications and source records attributed to B Malone.

At least 55 records · Page 3Linked to original sources
PubMed1984

Increased biosynthesis of platelet-activating factor in activated human eosinophils.

1-Alkyl-2-lyso-sn-glycero-3-phosphocholine:acetyl-CoA acetyltransferase catalyzes the conversion of biologically inactive lysophospholipid to bioactive platelet-activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) by an acetylation reaction. The activity of this enzyme in eosinophils isolated from patients with eosinophilia is stimulated (up to 4-fold) in a dose-, time-, and Ca2+/Mg2+-dependent manner after exposure to the eosinophil chemotactic factor of anaphylaxis (ECF-A), C5a, formyl-methionylleucylphenylalanine (fMLP), or ionophore A23187. The three naturally occurring chemotactic factors (ECF-A, C5a, and fMLP) cause a rapid and transient increase of enzyme activity, with a maximum at 1 or 3 min, whereas ionophore A23187 maintains an elevated level for up to 15 min. The activity of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine acetylhydrolase, an enzyme that catalyzes the breakdown of PAF to lyso-PAF, is not affected by C5a, fMLP, or ionophore A23187. The presence of PAF in eosinophils was established by demonstrating the lipid nature of the compound, the RF value being identical with that of synthetic 1-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine on thin layer chromatograms, and by its ability to induce serotonin release from rabbit platelets. Furthermore, ECF-A, C5a, fMLP, and ionophore A23187 all induce the secretion of PAF from eosinophils. These findings suggest that the generation and release of PAF could be a consequence of eosinophil chemotactic activation and may thus function in inflammatory and allergic reactions in which eosinophils participate.

Acetyltransferases↗
PubMed1983

Stimulation of calcium uptake by 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor) in rabbit platelets: possible involvement of the lipoxygenase pathway.

1-Alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor) induces an increase of Ca2+ uptake in rabbit platelets. This process depends upon the extracellular concentration of Ca2+ with the maximum stimulation occurring at 1-3 mM; uptake under these conditions is blocked by verapamil, a calcium-entry blocker. Increase of calcium uptake by the bioactive phospholipid was independent of ADP-induced platelet responses and of metabolites of arachidonic acid metabolism formed through the cyclooxygenase pathway. However, mepacrine, p-bromophenacyl bromide, eicosatetraynoic acid, and nordihydroguaiaretic acid significantly or totally inhibited the stimulation of Ca2+ uptake by 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine. When arachidonic acid was given sufficient time to be metabolized to other products by the platelets, stimulation of Ca2+ uptake also occurred. Arachidonic acid and platelet-activating factor did not produce an additive or synergistic effect. Our data suggest that a metabolite(s) generated from arachidonic acid through the lipoxygenase pathway may be the mediator(s) responsible for the action of platelet-activating factor in the induction of increased Ca2+ uptake in rabbit platelets.

Adenosine Diphosphate↗
PubMed1982

Structural features of platelet activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) required for hypotensive and platelet serotonin responses.

A number of analogs similar in structure to biologically active 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet activating factor) were tested for their relative effectiveness in lowering the blood pressure of spontaneous hypertensive rats and in releasing [3H]serotonin from rabbit platelets. Except for some minor variations, the two test systems gave the same pattern of relative responses for a given analog. Both biological activities (the antihypertensive response and release of platelet serotonin) appear to be stereospecific since the unnatural isomer exhibited no detectable effects. Other structural modifications that greatly reduced (greater than 500-fold) or eliminated the two biological activities were: 1) removal of the acetate group, 2) substitution of the acetate group with long-chain acyl, methoxy, benzoxy, N-formyl, N-trifluoroacetyl, N-hexadecanoyl, or deoxy groups such as dimethyl, propyl, isopropyl, or isobutyl, and 3) replacement of the sn-1 0-alkyl group with an acyl moiety. Biological activities were reduced to a lesser extent (100- to 500-fold) when the sn-2 carbon contained butyrate or hexanoate groups or if ethanolamine was substituted for the choline base. Replacing the sn-2 acetate group with an ethoxy group lowered the activity 48- and 120-fold for the blood pressure and serotonin release, respectively. Substitution of propionate for acetate at the sn-2 carbon gave a compound that was at least, if not more, biologically active than the parent structure; although an N-acetyl analog possessed biologic activities, the responses were only 0.27 to 1.0% of those obtained with the O-acetyl lipid. Maximum biological activity for both hypotensive effects and platelet serotonin release required a glycerolipid having an alkyl ether at the sn-1, acetate or propionate groups at the sn-2, and phosphocholine at the sn-3 positions.

Animals↗
PubMed1980

Enzymatic synthesis of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, a hypotensive and platelet-aggregating lipid.

1-Alkyl-2-acetyl-sn-glycero-3-phosphocholine, derived chemically from choline plasmalogens of beef heart, has been shown to possess powerful antihypertensive activity (Blank, M. L., Synder, F., Byers, L. W., Brooks, B., and Muirhead, E. E. (1979) Biochem. Biophys. Res. Commun. 90, 1194-1200) and to be an extremely potent platelet-activating factor (Demopoulos, C. C., Pinckard, R. N., and Hanahan, D. J. (1979) J. Biol. Chem. 254, 9355-9358). In the present study, microsomal preparations of rat spleen were shown to synthesize 1-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine by an acetyl-CoA:1-alkyl-2-lyso-sn-glycero-3-phosphocholine acetyltransferase reaction; the acetyltransferase appears to be different from the acyltransferase responsible for the transfer of palmitate to glycerolipids. The apparent Km for acetyl-CoA was 67 microM; the optimal concentration of 1-alkyl-2-lyso-sn-glycero-3-phosphocholine was 30 microM. Higher concentrations of the lyso substrate were inhibitory. When acetyl-CoA (100 microM) and 1-hexadecyl-sn-glycero-3-phosphocholine (30 microM) were incubated wih spleen microsomes under optimal conditions, the specific activity was approximately 10 nmol of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine/min/mg of protein. Although the reaction was inhibited by the addition of EDTA or EGTA to the incubation mixture, the acetyltransferase did not appear to require a divalent cation. An acyl analog, 1-palmitoyl-2-lyso-sn-glycero-3-phosphocholine, also served as a substrate for the acetyltransferase; however, the unnatural isomer, 3-alkyl-2-lyso-sn-glycero-1-phosphocholine, did not. The acetyltransferase activity was found in a variety of tissues, but the spleen had the highest activity of the tissues examined; lung, lymph nodes, and thymus also had high activities. Identification of the product and the possible physiological importance of the pathway are discussed.

Acetyltransferases↗
PubMed1979

Acyl-CoA reductase specificity and synthesis of wax esters in mouse preputial gland tumors.

Long-chain alcohols are synthesized in the mouse preputial gland tumor (ESR-586) by NADPH:acyl-CoA oxidoreductase. In this study, a series of labeled acids was tested as substrates for the oxidoreductase in a cell-free system from the tumor, and the distribution of label into alcohols, waxes, and other products was determined. The system contained the labeled acid, an acyl-CoA-generating system, an NADPH-generating system, and tumor homogenate. The highest rates of alcohol synthesis were obtained with palmitic (16:0), heptadecanoic (17:0), stearic (18:0), myristic (14:0), elaidic (18:1 trans), and linoleic (18:2) acids, which yielded, respectively, 151, 124, 102, 76, 65, and 35 pmol alcohol/min per mg protein. Decanoic (10:0), lauric (12:0), oleic (18:1 cis), linolenic (18:3), arachidonic (20:4), and behenic (22:0) acids all gave lower activities. Acyl-CoA formation did not appear to be rate limiting with any of the substrates tested except behenic acid. In addition to the fatty alcohol product, a small amount of fatty aldehyde was formed in the system. Incorporation of the labeled fatty acids into wax esters was examined and the distribution of label between the alcohol and acid components of the waxes was determined. Incubation of [1-(14)C]palmitic acid yielded 3.4% free alcohol, 8.3% alcohol esterified in waxes, and 7.7% palmitoyl groups esterified into waxes, whereas, at the other extreme, [1-(14)C]linolenic acid yielded 0.8%, 0.6%, and 38%, respectively, into the homologous components.-Wykle, R. L., B. Malone, and F. Snyder. Acyl-CoA reductase specificity and synthesis of wax esters in mouse preputial gland tumors.

Animals↗
PubMed1976

Transfer of methyl groups from N-dimethylnitrosamine to glycerolipids in rat liver.

We have examined the in vivo labeling of lipids after a single intraperitoneal injection of the carcinogen, (C14) dimethylnitrosamine, into rats. Liver was most active in incorporating (C14) methyl groups into lipids (0.91% of the injected dose) and 80% of the activity appeared in sn-3-phosphatidyl-choline. Chromatographic analysis of the products (and derivatives) formed after treatment of the (C14) phosphatidylcholine with phospholipase A2 (EC 3.1.1.4) and phospholipase C (EC 3.1.4.3) demonstrated that 89% of the radioactivity was in the choline moiety. These results indicate the transfer of methyl groups to lipids occurred via the lipid methylation pathway that converts phosphatidylethanolamine to phosphatidylcholine.

Animals↗