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Biomedical subjects

R M Kramer

Publications and source records attributed to R M Kramer.

At least 55 records · Page 3Linked to original sources
PubMed1985

The future of the voluntary agency in a mixed economy.

The growing reliance of voluntary nonprofit organizations on governmental funds ties their future to the fate of the welfare state. A mixed, three-sector, social service economy has blurred organizational differences and made a more rational division of responsibility unlikely. This article suggests that the traditional roles of voluntary agencies can still be reformulated to suggest a more realistic view of their distinctive areas of competence and vulnerability. To avoid goal deflection in the future, the author concludes that voluntary agencies must cope effectively with the dilemmas of entrepreneurialism and vendorism.

Financing, Government↗
PubMed1984

Metabolism of platelet-activating factor in human platelets. Transacylase-mediated synthesis of 1-O-alkyl-2-arachidonoyl-sn-glycero-3-phosphocholine.

The present study demonstrates that inactivation of exogenous 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (alkylacetyl-GPC; platelet-activating factor) by human platelets is mediated by the sequential action of two enzymes, 1) a Ca2+-independent acetylhydrolase recovered in the cytosolic fraction of platelets that deacylates alkylacetyl-GPC forming alkyllyso-GPC and 2) a CoA-independent, N-ethylmaleimide-sensitive transacylase associated with platelet membranes that incorporates a long-chain fatty acid into alkyllyso-GPC to produce alkylacyl-GPC. Separation of platelet phospholipids and subsequent resolution into individual molecular species by high-performance liquid chromatography revealed that the newly formed alkylacyl-GPC was exclusively alkylarachidonoyl-GPC and that the arachidonoyl group for acylation of alkyllyso-GPC was provided by phosphatidylcholine. We conclude that the previously described platelet arachidonoyl transacylase (Kramer, R.M., and Deykin, D. (1983) J. Biol. Chem. 258, 13806-13811) may play an important role in the metabolism of platelet-activating factor.

Acyltransferases↗
PubMed1984

Coenzyme A-mediated arachidonic acid transacylation in human platelets.

Platelet membranes contain two distinct transacylase activities catalyzing the synthesis of arachidonoyl phosphatides by acylation of added lysophosphatides with endogenous esterified arachidonate. In the absence of CoA, arachidonate is incorporated only into ethanolamine lysophosphatides with a high preference for the plasmalogen form (Kramer, R. M., and Deykin, D. (1983) J. Biol. Chem. 258, 13806-13811). In the presence of CoA, however, lysophospholipids are acylated in the order 1-acyl-lysophosphatidylserine greater than 1-acyl-lysophosphatidylethanolamine greater than 1-acyl-lysophosphatidylinositol. The CoA-mediated transacylation reaction was characterized with 1-acyl-lysophosphatidylserine as acyl acceptor. It was highly specific for arachidonate and preferentially used phosphatidylcholine as the arachidonoyl donor. This enzymatic pathway may be part of a deacylation-transacylation cycle for remodeling of phospholipids synthesized de novo (according to the Lands pathway) representing a mechanism for enrichment of phospholipids with arachidonic acid.

Acylation↗
PubMed1984

Effects of group identity on resource use in a simulated commons dilemma.

In a review of research on in-group categorization and group identity, Brewer (1979) proposed that cooperative solutions to social dilemmas, such as Hardin 's (1968) "tragedy of the commons ", may be achieved by exploiting the positive consequences arising from a common social-group identity. Three laboratory experiments were conducted to assess the effects of making salient either a superordinate (collective) or subordinate (differentiating) group identity in heterogeneous groups. In the first two experiments, naturally occurring social categories were used as a basis for group differentiation. In the third, the level of social-group identity was manipulated by varying the common fate of the group members. It was predicted that individual restraint would be most likely when a superordinate group identity was made salient and under conditions in which feedback indicated that the common resource was being depleted. Results from all three experiments provide support for this general hypothesis, indicating that cooperative responding is enhanced even when the basis for superordinate group identity is minimal.

Cooperative Behavior↗
PubMed1983

Arachidonoyl transacylase in human platelets. Coenzyme A-independent transfer of arachidonate from phosphatidylcholine to lysoplasmenylethanolamine.

Human platelets contain an enzyme that catalyzes CoA-independent release of arachidonic acid from phosphatidylcholine with concomitant incorporation into plasmenylethanolamine. Addition of lysoplasmenylethanolamine (10-80 microM) to a crude membrane preparation of prelabeled platelets (0.24 mg of protein/ml) induces transfer of [3H]arachidonate from endogenous phosphatidylcholine to lysoplasmenylethanolamine (0.8 nmol of arachidonic acid/min/mg of protein). The transacylation reaction occurs in the absence of Ca2+, has a broad pH optimum from 7 to 8, is not affected by excess unlabeled arachidonic acid, and is inhibited by N-ethylmaleimide (0.2 mM) and Triton X-100 (0.1 mg/ml). The enzyme shows a high specificity toward the acyl donor (phosphatidylcholine), transfers fatty acids in the order: arachidonic greater than eicosatrienoic greater than oleic, and preferentially acylates lysoplasmenylethanolamine but also other lysophosphatides (lysophosphatidylethanolamine greater than lysophosphatidylserine greater than lysophosphatidylinositol = 0). Platelet acyltransferase, on the other hand, acylates ethanolamine lysophosphatides with free arachidonic acid in the order: lysophosphatidyl-ethanolamine greater than lysoplasmenylethanolamine. These results suggest that a distinct acylation mechanism exists for introduction of arachidonic acid into plasmalogen phosphatides. In stimulated platelets, the transacylase may play an additional role in the controlled release of esterified arachidonic acid for synthesis of the biologically active oxygenated metabolites.

Acyltransferases↗
PubMed1982

Effect of membrane cholesterol on phospholipid metabolism in thrombin-stimulated platelets. Enhanced activation of platelet phospholipase(s) for liberation of arachidonic acid.

The cholesterol to phospholipid mole ratio (C/PL) of human platelets was increased 1.3-fold or maintained at a normal value by incubating platelets with sonicated dispersions of cholesterol and phosphatidylcholine (PC) (C/PL = 3 or 1, respectively). Thrombin-induced mobilization of [3H]arachidonic acid from prelabeled phospholipids and subsequent formation of labeled cyclo-oxygenase and lipoxygenase products were increased in cholesterol-enriched platelets as a function of thrombin concentration. Elevated platelet cholesterol content affected thrombin-induced changes in platelet phospholipids: (a) hydrolysis of PC was more sensitive to thrombin and was markedly enhanced over a wide range of thrombin concentrations (0.1-2 units/ml); (b) hydrolysis of phosphatidylinositol (PI) was increased at thrombin concentrations greater than or equal to 0.2 unit/ml. Increased metabolism of [3H]arachidonic acid in stimulated cholesterol-enriched platelets was due to loss of [3H]arachidonate from PC at 0.1 unit/ml of thrombin. At higher thrombin concentrations (0.2-2 units/ml) it reflected enhanced hydrolysis of predominantly PC, but also PI. We conclude that cholesterol, possibly through its effect on platelet lipid organization, influences arachidonic acid metabolism in stimulated plates by promoting enhanced activity of platelet phospholipase(s) for liberation of arachidonic acid.

Arachidonic Acids↗
PubMed1981

Rapid transmembrane movement of phosphatidylcholine in small unilamellar lipid vesicles formed by detergent removal.

Small unilamellar phosphatidylcholine vesicles, formed by solubilizing phosphatidylcholine with sodium cholate and removing the detergent by gel filtration, have been studied in their interaction with phospholipid exchange protein. The exchange of phosphatidylcholine between the vesicles and erythrocyte ghosts was greatly stimulated by the phosphatidylcholine-specific exchange protein from bovine liver. It was found that 95% of the phosphatidylcholine was readily available for exchange within 3 h at 37 degrees C. In similar vesicles prepared by sonication only 70% of the phosphatidylcholine was rapidly exchangeable. Our results indicate that the transmembrane movement of phosphatidylcholine across the bilayer of vesicles prepared by the cholate technique is a relatively fast process. The results are discussed with respect to the presence of trace amounts of lipid-associated cholate which may facilitate the transbilayer exchange of phosphatidylcholine.

Animals↗
PubMed1980

Transbilayer mapping of membrane proteins using membranes isolated on polylysine-coated polyacrylamide beads.

Erythrocyte and HeLa cell plasma membranes were isolated on polylysine-coated polyacrylamide beads and the transbilayer disposition of their proteins was investigated. When membranes of intact erythrocytes were isolated on beads and then labelled by lactoperoxidase-catalysed iodination, their labelling pattern was similar to that of inside-out vesicles in solution. When the membranes of intact HeLa cells were isolated on beads and then labelled by galactose oxidase-[3H]borohydride treatment, no glycoprotein or glycolipid sugars were accessible. On the other hand, when the HeLa cell membranes were isolated on beads and then labelled by the lactoperoxidase-catalysed iodination, all of the major membrane proteins were iodinated. These experiments confirmed for HeLa cell membranes what had previously been shown for erythrocyte membranes: when the membranes of intact cells are isolated on beads, the accessibility of their surfaces to enzymatic probes is the same as would be expected of inside-out vesicles in suspension. Double-label experiments, in which the HeLa cell membranes were labelled first on the intact HeLa cells and again after isolation on beads, identified several proteins which may span the membrane.

Borohydrides↗
PubMed1979

Retention of lipid asymmetry in membranes on polylysine-coated polyacrylamide beads.

Phosphatidylcholine-specific exchange protein from calf liver was used to study the asymmetry and transmembrane movement of phosphatidylcholine in rat erythrocyte membranes isolated on polylysine-coated beads. While confirming previously published results for sealed ghosts, we found that for membranes attached to beads, where the cytoplasmic surface is exposed, about 36% of the total phosphatidylcholine is readily available for exchange, while the remaining 64% is exchangeable at a much slower rate. This indicates that the relative transbilayer asymmetry of phosphatidylcholine is largely maintained when red cell membranes are isolated on beads. On the other hand, transmembrane movement of phosphatidylcholine is decreased in membranes attached to cationized beads: the half-time for equilibration of phosphatidylcholine between the two monolayers of the membrane is 8 h for membranes on beads, compared to 1.5 h for sealed ghosts. Our results indicate that polylysine-derivatized beads are a useful tool for studying asymmetric properties of biological membranes.

Acrylamides↗
PubMed1979

Voluntary agencies in four welfare states.

Although the development of democratic welfare states has not led to the decline of non-governmental (voluntary) social service agencies, the future survival of voluntarism and pluralism is still a cause of concern. An exploratory comparative analysis of voluntary agencies serving the physically and mentally handicapped in the U.S., England, The Netherlands, and Israel provides some empirical data on the effects of selected environmental and organizational variables on the ability of voluntary agencies to innovate, provide supplementary services, and promote citizen participation and social change. The findings, which tend to support theories of convergence of modern societies, suggest hypotheses regarding the distinctive competence and vulnerability of voluntary agencies as an organizational hybrid in between a voluntary association and a service bureaucracy.

Persons with Disabilities↗
PubMed1976

Comparison of the redox bioassay with other assays for luteinizing hormone.

The cytochemical (redox) bioassay for LH has been compared with established LH assays. Measurements made by redox bioassays were considerably lower than those made by radioimmunoassay in human female plasma samples obtained at mid-cycle. There was no apparent relationship between measurements on incubation media from cultures of sheep pituitary glands made by redox bioassay and the ovarian ascorbic acid depletion (OAAD) assay. After polyacrylamide gel electrophoresis of a crude extract of a human pituitary gland, redox LH measurements were lower than those of the OAAD assay and radioimmunoassay in the cathodal segments of the gel. By contrast, there was reasonable agreement between LH measurements made by radioimmunoassay and redox assay in cathodal fractions from gel electrophroesis of a purified pituitary LH preparation. Follicle-stimulating hormone, and the alpha- and beta-subunits of LH depressed the response of intact LH in the redox assay; this might explain the relatively low levels of LH measured by redox assay in some of the experiments described. Which type of assay best reflects the biological activity of LH in man remains to be determined.

Animals↗