186,540 research outputs found
Heparin-induced structural and functional alterations of bovine trypsin.
No full textTo investigate the mechanism whereby heparin can modulate the activity of serine proteinases, bovine trypsin was chosen as reference and treated with heparin at 10, 100 and 200 μg/ml, in buffer solvents, with and without incubation at 37°C. Heparin caused rapid, buffer- and pH-dependent decrease in trypsin solubility due to the generation of insoluble fragments from proteinase. Desalting treatments variously restored solubility by removing insoluble material. UV absorption and fluorescence emission spectra revealed significant heparin-induced conformational alterations in the trypsin molecule, the maximal effect being apparent at a proteinase-to-heparin molar ratio ranging from 1.6 to 1.0. The involvement of the catalytic sites of trypsin by heparin was further confirmed by the significant reduction in the difference absorption spectra of proflavine. Both proteolytic and esterolytic activities of trypsin were shown to be markedly decreased by heparin, especially after 5 h incubation at 37°C. However, when the proteolytic and esterolytic activities of trypsin were measured on fresh solutions not submitted to desalting treatments, variable activation instead of inhibition of both activities was observed in the presence of heparin, this effect waning spontaneously in time or after desalting treatment. The paradoxical increase in functional activities was not inhibited by soybean trypsin inhibitor and was accompanied by denaturation and fragmentation of the proteinase as demonstrated by spectroscopic analyses and SDS-PAGE of fresh solutions. The results obtained indicate that heparin causes a rapid, time- and temperature-dependent conformational alteration of trypsin with irreversible denaturation and degradation of the proteinase. The underlying mechanism appears to be heparin-catalyzed oxidative degradation of trypsin due to liberation of oxygen radicals which are also responsible for the temporary increase in catalytic functions
Canrenone as a partial agonist at the digitalis receptor site of (Na+-K+)ATPase
No full textCanrenone, a spironolactone metabolite, was tested for its possible effects on (Na+-K+) adenosine triphosphatase (ATPase) activity [Mg++-dependent, (Na+-K+)-activated ATP phosphohydrolase (E.C.3.6.1.3) and ouabain interaction with the enzyme. Canrenone competitively antagonized the binding of [3H]ouabain to (Na+-K+)ATPase and inhibited (Na+-K+)ATPase activity. The multiple inhibition technique was used to demonstrate that canrenone is a partial inhibitor of (Na+-K+)ATPase, mutually exclusive with respect to ouabain. Comparative studies of the effects of ouabain and canrenone on potassium-dependent p-nitrophenylphosphatase activity (E.C.9.6.1.7) and potassium activation of (Na+-K+)ATPase confirmed that ouabain and canrenone interacted with the same receptor site. The finding that canrenone is a partial agonist may explain the results of previous in vivo studies showing that spironolactone and the allied drug to potassium conrenoate have either a positive inotropic action or an antagonistic effect against digitalis toxicity
Differential effects of heparin and glucose on structural conformation of human alpha1-antitrypsin: evidence for a heparin-induced cleaved form of the inhibitor.
No full textalpha1 Antitrypsin (alpha1AT) is the archetypal member of the serpin superfamily. Current knowledge of its inhibitory mechanism does not provide for any heparin-induced enhancement of serine proteinase inhibition. Since previous results have shown that an apparently altered alpha1AT form may be purified from the plasma of insulin-dependent diabetics by means of heparin-affinity chromatography, in the present work the possibility was tested that heparin at various concentrations modifies the structural conformation and function of human alpha1AT in the absence and presence of glucose, used at concentrations of 15 mM to mimick mild hyperglycemic conditions. Heparin was observed to bind strongly to alpha1AT, causing maximal enhancement of tryptophan fluorescence emission at 50 microg/ml, mostly in the presence of glucose. Circular dichroism spectra revealed that heparin with glucose caused the most relaxed, ordered structure of the inhibitor with increased heat stability. Modification in conformation was accompanied by loss of inhibitory activity, as demonstrated by the inability of alpha1AT to block bovine trypsin in the specific assay and by alterations of its immunological properties. However, despite inactivation, in the presence of heparin-both with and without glucose-alpha1AT was still able to bind trypsin, as revealed by inhibitor-to-proteinase complexes visible in both SDS- and nondenaturing electrophoreses. These complexes showed the same feature regardless of trypsin concentration and differed from those formed at a molar excess of the inhibitor in the absence of heparin, since they underwent rapid, intense fragmentation accompanied by complete loss of the secondary structure of the inhibitor. Even in the absence of trypsin, cleavage of alpha1AT was also observed to occur at both Val321- and Glu344- in the primary sequence of the inhibitor in the presence of 50 microg/ml heparin, with and without glucose. These results suggest that heparin binding to alpha1AT causes profound structural changes in the molecule, involving both the expulsion of the reactive site out of the molecule plane and a relaxed, heat-stable form of the inhibitor, rendered a substrate for the proteinase. Although glucose apparently does not affect alpha1AT functioning, it does enhance the effects of heparin on the alpha1AT structure. The possibility is discussed that, while heparin and glucose binding occurs at different sites on alpha1AT, glucose favors heparin binding by inducing a partially relaxed form in the inhibitor. Differences in structure and charge between the two substances account for both different individual effects on alpha1AT and the predominance of the effects of heparin
Alteration of plasma proteinase-antiproteinase system in type 1 diabetic patients. Influence of sex and relationship with metabolic control.
No full textThe aim of the present study was to investigate whether or not alterations of the plasma proteinase-antiproteinase system were present in type 1 (insulin-dependent) diabetic patients and, if so, whether or not they were related to sex, age at onset and duration of the disease as well as to short- and long-term diabetic control. The plasma concentration of trypsin-like activity and two of the most important plasma serine proteinase inhibitors, alpha 1-antitrypsin and alpha 2-macroglobulin, were determined in 95 type 1 diabetic and 67 control subjects. The plasma concentration of alpha 1 antitrypsin was found to be markedly decreased (P < 0.001), whereas plasma alpha 2-macroglobulin and trypsin-like activity were increased in diabetics compared to controls (P = 0.009 and < 0.001, respectively). Sex also influenced the values of both proteinase inhibitors in diabetics, women showing higher values of plasma alpha 1-antitrypsin (P = 0.004) than men. In women, HbA1c was also positively correlated with blood glucose (P < 0.001), daily insulin dosage (P < 0.001), and trypsin-like activity of plasma (P = 0.02). On the contrary, in men, HbA1c appeared to be negatively correlated with plasma alpha 2-macroglobulin (P = 0.02). In addition to sex, age at onset (but not duration) of the disease revealed differences in plasma alpha 1-antitrypsin among diabetics, the lowest mean value of this inhibitor being present in men with age at onset below 15 years, who also showed a significant negative correlation between this inhibitor and HbA1c (P = 0.01)
Reduction by eparin of basal and glucose-induced increase in proteolytic activity of trypsin.
No full textPurification of proteinase-like and Na+/K(+)-ATPase stimulating substance from plasma of insulin-dependent diabetics and its identification as alpha 1-antitrypsin
No full textThe purpose of this study was to purify and identify the proteinase-like substance previously recognized as responsible for the Na+/K(+)-ATPase stimulating property of plasma from insulin-dependent diabetic subjects. Anion-exchange chromatography followed by two-step heparin affinity chromatography resulted in a fraction highly enriched in both potent Na+/K(+)-ATPase stimulating activity and potent proteolytic activity. Approx. 400 micrograms of purified protein was isolated from 62 mg of starting plasma proteins. When analyzed on sodium dodecyl sulfate gels the active fraction consisted mainly of one polypeptide band with an apparent molecular mass of 66 kDa under either reducing or nonreducing conditions. The proteinase-like properties of the purified fraction were further revealed by its ability to clot plasma, split fibrinogen with production of fibrinopeptide A and induce shape change in human platelets and irreversible platelet aggregation in the presence of the stable analogue of endoperoxides U46619. Its additional capacity to affect platelet phosphoinositol metabolism was shown by the stimulation of protein kinase C-dependent phosphorylation of 47 kDa platelet membrane protein. In designing an identification protocol for the purified fraction, it was postulated that plasma proteinases are probably bound to their inhibitors, to form a stable covalently linked complex. The possibility that a proteinase-proteinase inhibitor complex was purified instead of single proteinase(s) was investigated. Neither trypsin nor neutrophil elastase were present in the active fraction whereas, among the possible plasma proteinase inhibitors tested, immunoreactivity was observed only in the presence of alpha 1-antitrypsin (alpha 1 AT) antiserum. Double immunodiffusion showed that control human alpha 1 AT and the plasma-purified fraction shared common antigens. Furthermore, both isoelectric focusing and amino acid composition analysis showed that the two substances were similar. The results obtained indicate that alpha 1 AT is apparently the only active component of the purified fraction from the plasma of insulin-dependent diabetics, thus suggesting that an altered form of the inhibitor is responsible for the broad range of proteinase-like effects elicited by the plasma-purified fraction
Reduction of erythrocyte (Na+-K+)ATPase activity in type 1 (insulin-dependent) diabetic subjects and its activation by homologous plasma.
No full textThe (Na+-K+)ATPase and (Mg2+)ATPase activities of erythrocyte membranes of Type 1 (insulin-dependent) diabetic patients were found to be significantly reduced compared to matched controls (p less than 0.005). On the contrary, erythrocyte Na+ and K+ contents were similar in diabetic patients and in normal subjects. When erythrocyte membranes from diabetic patients were incubated with their own plasma, a significant increase was observed in sodium-potassium ATPase activity (p less than 0.005), whereas (Mg2+)ATPase activity was not affected. The plasma stimulatory effect showed saturation kinetics. Maximum average stimulation was 96% (+/- 21.3). A similar stimulation pattern, although more limited in extent (maximum 48.3% +/- 12.2), was found when erythrocyte membranes from normal subjects were incubated with diabetic plasma. Normal plasma exhibited a modest stimulatory effect on erythrocyte (Na+-K+)ATPase activity. Similar stimulatory effects by diabetic plasma were observed on a (Na+-K+) ATPase preparation from beef heart. It is proposed that diabetic plasma contains a specific (Na+-K+)ATPase activator in a higher concentration than normal plasma. This may explain why a normal cellular electrolyte content was found in diabetic erythrocytes in spite of a reduced Na+-K+ pump activity. Purification experiments indicate that the plasma activator is a protein with a molecular weight greater than 50,000. Both the (Na+-K+)ATPase activity and the stimulatory effect of diabetic plasma were not influenced by the metabolic control, since they did not correlate significantly with fasting blood glucose and daily insulin dosage. Moreover, no correlation was found with duration of diabetes or age at diagnosis of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS
Effects of aprindine on the electromechanical coupling of the myocardium and smooth muscle
No full textAuthor-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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