Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phosphatidylserine (PS) in the plasma membrane of nonactivated human platelets is almost entirely located on the cytoplasmic side. Stimulation of platelets with the Ca2+ ionophore A23187 or combined action of collagen plus thrombin results in a rapid loss of the asymmetric distribution of PS. Also, treatment with the sulfhydryl-reactive compounds diamide and pyridyldithioethylamine (PDA) causes exposure of PS at the platelet outer surface. PS exposure is sensitively measured as the catalytic potential of platelets to enhance the rate of thrombin formation by the enzyme complex factor Xa-factor Va, since this reaction is essentially dependent on the presence of a PS-containing lipid surface. In this paper we demonstrate that endogenous PS, previously exposed at the outer surface during cell activation or sulfhydryl oxidation, can be translocated back to the cytoplasmic leaflet of the membrane by addition of dithiothreitol (DTT) but not by nonpermeable reducing agents like reduced glutathione. Treatment of platelets with trypsin or chymotrypsin, prior to addition of DTT, inhibits the inward transport of exposed PS. Moreover, severe depletion of metabolic ATP, as obtained by platelet stimulation with A23187 in the presence of metabolic inhibitors, though not inhibiting PS exposure at the outer surface, blocks the translocation of endogenous PS to the internal leaflet of the plasma membrane. These results strongly indicate the involvement of a membrane protein in the inward transport of endogenous PS. Recently, an aminophospholipid-specific translocase in the platelet membrane was postulated on the basis of the inward transport of exogenously added PS (analogues) [Sune, A., Bette-Bobillo, P., Bienvenue, A., Fellmann, P., & Devaux, P.F. (1987) Biochemistry 26, 2972-2978].(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Exposure of endogenous phosphatidylserine at the outer surface of stimulated platelets is reversed by restoration of aminophospholipid translocase activity. 273 Aug 70

Purified membrane-associated phosphatidylinositol synthase (CDP diacylglycerol:myo-inositol 3-phosphatidyltransferase, EC 2.7.8.11) from Saccharomyces cerevisiae was reconstituted into unilamellar phospholipid vesicles. Reconstitution of the enzyme was performed by removing detergent from an octylglucoside/phospholipid/Triton X-100/enzyme mixed micelle mixture by Sephadex G-50 superfine column chromatography. The average diameter of the vesicles was 40 nm and chymotrypsin treatment of intact vesicles indicated that over 90% of the reconstituted enzyme had its active site facing outward. The enzymological properties and reaction mechanism of reconstituted phosphatidylinositol synthase were determined in the absence of detergent. The reconstituted enzyme was used as a model system to study the regulation of activity. Phosphatidylinositol synthase was constitutive in wild type cells grown in the presence of water-soluble phospholipid precursors as determined by enzyme activity and immunoblotting. Reconstituted enzyme was not effected by water-soluble phospholipid precursors or nucleotides. Maximum activity was found when the enzyme was reconstituted into phosphatidylcholine: phosphatidylethanolamine: phosphatidylinositol: phosphatidylserine vesicles. Phosphatidylserine stimulated reconstituted activity, suggesting that the local phospholipid environment may regulate phosphatidylinositol synthase activity.
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PMID:Phosphatidylinositol synthase from Saccharomyces cerevisiae. Reconstitution, characterization, and regulation of activity. 300 84

The activity of chymase was markedly inhibited by phosphoglycerides such as phosphatidic acid, phosphatidylserine, and phosphatidylinositol, but was not affected by acylglycerides, phosphoglyceroserine, serine, inositol, or glycerol. These results suggest that both the nonpolar hydrophobic hydrocarbon tails and the polar hydrophilic head are essential for the inhibitory effects of phosphoglycerides. Binding of a primary amine to an anionic polar head of phosphatidic acid, such as in phosphatidylserine and phosphatidylethanolamine, slightly decreased the inhibitory effect of phosphatidic acid and, conversely, binding of a strong cation to the head, such as in phosphatidylcholine, resulted in its activation of chymase. Phosphatidic acid containing an unsaturated fatty acid, such as dioleoyl phosphatidic acid, caused the same extent of inhibition as natural phosphatidic acid from bovine brain, but was 20 times more inhibitory than phosphatidic acid containing a saturated fatty acid, such as distearoyl phosphatidic acid. The inhibition by phosphatidylserine was noncompetitive and pseudoirreversible, and the Ki value was 0.54 microM. The inhibition of chymase by phosphatidylserine was pH dependent, being strong at pH 8.5 to 9.5 but weak below pH 7.5. Phosphatidylserine specifically inhibited chymase and elastase; it did not inhibit the other chymotrypsin-type serine endopeptidases tested, trypsin, papain, collagenase, carboxypeptidase A, or cathepsin D.
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PMID:Inhibition of chymase activity by phosphoglycerides. 388 53

Phosphatidylserine, in contrast with other phospholipids, markedly enhanced histamine release from rat peritoneal mast cells induced by dextran or protein antigens. This enhancing effect was selective for dextran and protein antigens and did not extend to the action of compound 48/80 or chymotrypsin. These findings suggest a role for phosphatidylserine in the response of mast cells to antigens.
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PMID:Phosphatidylserine: selective enhancer of histamine release. 410 49

Effects of membrane phospholipids on Na(+)-Ca2+ exchange and Na+ channel currents were studied in giant excised cardiac sarcolemmal patches. Phospholipids were suspended in an inert vehicle of alpha-tocopherol acetate and hexane and were then directly applied to the side of patch electrodes at a short distance from the tip during current recording. Phosphatidylserine strongly stimulated outward Na(+)-Ca2+ exchange current and altered the kinetics of cytoplasmic Na(+)- and Ca(2+)-dependent secondary modulation. This effect was partially reversed by phosphatidylcholine. Prolonged treatment with phosphatidylserine eliminated the inactivation transient normally observed upon rapid application of cytoplasmic Na+ but left cytoplasmic Ca2+ dependence largely intact. In such cases, subsequent chymotrypsin treatment removed cytoplasmic Ca2+ dependence, but had no further stimulatory effect, indicating maximum alleviation of inactivation by phosphatidylserine. While these results indicate that phosphatidylserine acts on a cytoplasmic, protease-sensitive regulatory domain of the exchanger, phosphatidylserine also stimulated the exchange current after deregulation by chymotrypsin, indicating an effect on the exchange mechanism itself. As in other myocyte preparations, cardiac Na+ currents in giant patches undergo a time-dependent negative shift in the voltage dependence of steady-state inactivation. Loss of phosphatidylserine from the cytoplasmic leaflet (i.e. loss of transbilayer asymmetry of phosphatidylserine distribution) does not appear to be the underlying cause, since phosphatidylserine did not reverse this shift, despite stimulation of Na(+)-Ca2+ exchange current in the same patches.
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PMID:A novel method for direct application of phospholipids to giant excised membrane patches in the study of sodium-calcium exchange and sodium channel currents. 839 64