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41.
Disruption of the Primary Fouling Sequence on Fiber Glass-Reinforced Plastic Submerged in the Marine Environment 总被引:1,自引:1,他引:0
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Fiber glass-reinforced plastic immersed in an experimental estuarine mesocosm fouled at estimated rates of 0.5, 5.5, and 18.8 ng (wet weight) mm−2 day−1 over days 0 to 2, 2 to 6, and 6 to 14, respectively. Protists, dominated by diatoms, which developed between days 3 and 6 and covered 90% of the undisturbed surface in 2 weeks, were effectively removed by twice-weekly brushing of the surface to maintain an immature 3-day bacterial film which covered 12% or less of the surface and had a biomass 3 orders of magnitude smaller than surfaces with 2 weeks' unrestricted fouling. Direct brushing of the fiber glass-reinforced plastic tank walls of experimental estuarine mesocosms minimized the “wall effect” by keeping a surface that maintained a low biomass of a slowly accumulating bacterial film rather than a surface which supported the more rapid accumulation of protists which in turn may induce the settlement of invertebrates and macrophytes. 相似文献
42.
A highly potent beta-adrenergic antagonist based on the structure of alprenolol has been prepared by replacement of the isopropylamine residue of alprenolol by 1, 8-diamino-p-menthane (AlpM). The resulting mixture of isomers (AlpM) competes for occupancy of beta-adrenergic receptors in frog erythrocycte membranes with an apparent KD of 210 pM. The bromoacetylated derivative of AlpM (BrAlpM) leads to an irreversible inactivation of the [3H]dihydroalprenolol ([3H]DHA) binding sites. Various adrenergic agonists and antagonists afford specific and stereoselective protection of the receptor against inactivation by BrAlpM. Tritiation of AlpM followed by bromoacetylation and chromatographic separation yielded two isomers, Br-1-AlpM and Br-8-AlpM of high specific radioactivity (~ 40 Ci/mmol). Both radiolabelled isomers interacted specifically and with high affinity with the beta-adrenergic receptor, but only a small amount of the ligands could be covalently incorporated into the receptor subunit. This agent provides a powerful new probe for studies of beta-adrenergic receptors in analogy with bungarotoxin for the nicotinic cholinergic receptor. 相似文献
43.
The involvement of glycoconjugates in the insulin-receptor interactions in mouse liver is tested by digestions of membranes with various enzymes. Trypsin decreased the binding of [125I]insulin to liver membranes. After digestion with β-galactosidase no “high affinity” receptor sites could be detected. The effects observed with plant lectins confirm the involvement of galactoconjugates in the insulin binding process. Sophora japonica and Ricinus communis lectins (with galactose specificity) and concanavalin A largely inhibit the binding process of insulin and those effects concern the “high affinity” receptor sites. Other lectins (wheat germ agglutinin, Dolichos) and enzymes (α-l-fucosidase, ) are without effect on insulin binding.Comparative studies performed on diabetic mouse liver membrane (KK mice), previously characterized by decreased number of insulin receptors, are in good agreement with qualitatively similar receptor sites in both non-diabetic (control) and diabetic mice. Effects of enzymes and lectins yielded same results as compared to control membranes. Plasma membrane proteins and glycoproteins in both types of mouse are indistinguishable with respect to enzymic and chemical analysis. Sodium dodecyl sulphate acrylamide gel electrophoresis shows identical patterns. Moreover, the decrease in the number of insulin receptors is easily reversed with diet restriction. These data are consistent with the similarity of receptor sites in control and diabetic liver membrane. 相似文献
44.
N G Seidah R Routhier M Caron M Chrétien S Demassieux R Boucher J Genest 《Canadian journal of biochemistry》1978,56(9):920-925
In this paper, we present the amino-terminal sequence of rat tonin, an endopeptidase responsible for the conversion of angiotensinogen, the tetradecapeptide renin substrate, or angiotensin I to angiotensin II. It is shown that isoleucine and proline occupy the amino- and carboxy-terminal residues respectively. The N-terminal sequence analysis permitted the identification of 34 out of the first 40 residues of the single polypeptide chain composed of 272 amino acids. These results showed an extensive homology with the sequence of many serine proteases of the trypsin-chymotrypsin family. This information, coupled with the slow inhibition of tonin by diisopropylfluorophosphate, classified this enzyme as a selective endopeptidase of the active serine protease family. 相似文献
45.
Catecholamines substituted to agarose were synthesized in various ways. Norepinephrine and isoproterenol were linked to p-aminobenzamidohexyl agarose by an azo linkage to the catechol ring. Norepinephrine was also couple to hexyl agaros via the amino group, forming an amino, guanidino or amido bond. Biological activity of the immobilized catecholamines was determined by assessing their abilities to interact with adenylate cyclase in several membrane preparations and intact preparations of erythrocytes. In dog heart membranes, stimulation of adenylate cyclase by the catecholamine-gels could be accounted for by leached hormone which had been released from the gels. In frog erythrocyte membranes, leaching was minimal and no significant stimulation of adenylate cyclase was observed. Agarose-immobilized catecholamines, however, competitively inhibited isoproterenol stimulation of adenylate cyclase in these erythrocyte membranes indicating that catecholamines which are bound to agarose interact with the beta-adrenergic receptors as antagonists rather than agonists. When tested on intact frog erythrocytes, agarose immobilzed catecholamines did not increase the intracellular levels of cyclic AMP, although isoproterenol caused as 8-10 fold rise in these levels. Similarly, when tested for antagonist activity in the intact cells the agarose-catecholamines failed to inhibit the stimulation of cyclic AMP caused by isoproterenol. The difference observed in the beta-adrenergic antagonist activity of the agarose-bound catecholamines in membrane preparations and intact cells can be attributed to steric factors which could have prevented the access of the bead-bound ligands with the surface of the cell or to the possibility that receptors might be buried in the membrane matrix. 相似文献
46.
A spin label study of the thermal unfolding of secondary and tertiary structure in E. colic transfer RNAs. 总被引:3,自引:3,他引:0
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The molecular mechanism of thermal unfolding of E. coli tRNAGlu, tRNAfMet and tRNAPhe (in 0.02M Tris-HC1, pH 7.5. 10 MM Mg C12) has been examined by the spin-labeling technique. The rate of tumbling of the spin label has been measured as a function of temperature for ten different selectively spin-labeled tRNAs. Only spin labels at position s4U-8 were able to probe the tertiary structure. Evidences are presented which support the hypothesis that the thermal denaturation of the three species of tRNAs studied is sequential. The unfolding process occurs in three discrete stages. The first step (30 degrees-32 degrees) could either be assigned to a localized reorganization of the cold-denatured structure or to a "transient" melting, followed by the simultaneous disruption of the tertiary structure and part of the hU helix. This transition is observed even in the absence of magnesium. The second step (50 degrees-54 degrees) involves the melting of the anticodon and miniloop regions. The last step occurs above 65 degrees where the t psi c and amino acid acceptor stems, forming one continuous double helix, melt. A simple dynamic model is considered for tRNA function in protein biosynthesis. 相似文献
47.
The interaction of insulin with its receptors was studied in liver plasma membranes of the young non-obese hereditary diabetic mouse (KK strain). Under identical conditions of preparation and incubation, the membranes of the KK mouse bind only 55-70% as much insulin per mg of protein as those of the control mouse (Swiss albino). Scatchard analysis suggests that this decrease in binding is due to a decrease in the number of receptor sites in the membrane of the diabetic mouse. However, the membranes of diabetic and control mice do not exhibit significant differences in hexosamine and sialic acid contents, enzyme activities, and protein and glycoprotein analysis. The decrease in insulin receptors in the KK mouse seems to correlate with the insulin resistance which they exhibit. 相似文献
48.
Following I.V. injection of 3H-aldosterone, the rates of clearance of plasma 3H-radioactivity was demonstrated to be sex-dependent in intact rats. Even though the percentages of CH2Cl2-extractable plasma radioactivity are greater in female than in male rats, the quantities of CH2Cl2-extractable label are similar until 60 min post-injection. However, the quantities of non-extractable, polar metabolites of aldosterone (NEPD) are markedly greater in the plasma of males and rapidly reach peak levels 10 min post-injection of aldosterone. In females, these polar metabolites (NEPD) are rapidly cleared from the blood. After bile-duct cannulation, the rate of excretion of aldosterone radiometabolites was demonstrated to be rapid and sex-dependent. Within 1 hr., female rats excreted via the bile 82% of the injected dose of 3H-aldosterone, compared to 49% in male rats. In both sexes, greater than 95% of the total radioactivity excreted in the bile are non-extractable polar metabolites of aldosterone (NEPD). The sex hormones appear to influence not only the nature of metabolism of aldosterone in the liver, but also the rates of clearance of aldosterone and its metabolites from the plasma into the bile. 相似文献
49.
Phosphorylation sites on two domains of the beta 2-adrenergic receptor are involved in distinct pathways of receptor desensitization 总被引:19,自引:0,他引:19
W P Hausdorff M Bouvier B F O'Dowd G P Irons M G Caron R J Lefkowitz 《The Journal of biological chemistry》1989,264(21):12657-12665
Continuous exposure of cells to neurotransmitter or hormone agonists often results in a rapid desensitization of the cellular response. For example, pretreatment of Chinese hamster fibroblasts (CHW cells) expressing beta 2-adrenergic receptors (beta 2AR) with low (nanomolar) concentrations of isoproterenol, a beta-adrenergic agonist, causes decreases in the sensitivity of the cellular adenylyl cyclase response to the agonist, without changing the maximal responsiveness. In contrast, exposure of CHW cells to high (micromolar) concentrations of isoproterenol results in decreases in both sensitivity and the maximal responsiveness to agonist. To explore the role(s) of receptor phosphorylation in these processes, we expressed in CHW cells three mutant beta 2AR genes encoding receptors lacking putative phosphorylation sites for the cAMP-dependent protein kinase A and/or the cAMP-independent beta 2AR kinase. Using these mutants we found that exposure of cells to low concentrations of agonist appears to preferentially induce phosphorylation at protein kinase A sites. This phosphorylation correlates with the decreased sensitivity to agonist stimulation of the adenylyl cyclase response. At higher agonist concentrations phosphorylation on both the beta 2AR kinase and protein kinase A sites occurs, and only then is the maximal cyclase responsiveness elicited by agonist reduced. We conclude that low or high concentrations of agonist elicit phosphorylation of beta 2AR on distinct domains, with different implications for the functional coupling of the receptors with effector molecules. 相似文献
50.