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31.
Kotormán M Laczkó I Szabó A Simon LM 《Biochemical and biophysical research communications》2003,304(1):18-21
The effects of calcium ions on the conformation and catalytic activity of trypsin and alpha-chymotrypsin were studied in aqueous ethanol. The activity of alpha-chymotrypsin was practically lost within 10 min in the presence of 60% ethanol while trypsin preserved about 40% of its original activity even in 85% ethanol at pH 3. The catalytic activity of alpha-chymotrypsin did not decrease in the presence of 1.2M CaCl2 and 0.6M CaCl2 with trypsin in ethanolic solvent. In the latter case an activation of enzyme was observed. The stabilizing effects of calcium ions were accompanied by an increase in the helical content in both enzymes, as followed by circular dichroism measurements. 相似文献
32.
Dirk-Jan van Unen Johan F. J. Engbersen David N. Reinhoudt 《Journal of Molecular Catalysis .B, Enzymatic》2001,11(4-6):877-882
Studies on the mechanism of crown-ether-induced activation are described in this paper. Michaelis Menten kinetics of -chymotrypsin in toluene in the presence and absence of 18-crown-6 showed that only Vmax is increased upon crown ether treatment. Parallel Lineweaver–Burk plots indicate that crown ethers do not activate the enzyme by specific interactions in the active site, such as transition state stabilization or facilitated transport of water molecules. Increased Vmax values of crown-ether-treated enzyme most probably originate from conformational changes, which alter kcat as well as the amount of catalytically active enzyme. 相似文献
33.
Stable liposomes have been prepared from lipid mixture containing sucrose stearate-palmitate. 1.2 X 10(-4) mol of model enzyme alpha-chymotrypsin per mol of lipid have been coupled to prepared liposomes activated by periodate oxidation of sucrose units. 相似文献
34.
Elsa Abuin Eduardo Lissi Roxanna Duarte 《Journal of Molecular Catalysis .B, Enzymatic》2004,31(4-6):83-85
Results obtained on the effect of addition of dodecyltrimethylammonium bromide (DTAB) upon the α-chymotrypsin (α-CT) catalyzed hydrolysis of 2-naphthyl acetate (2-NA) under steady state conditions for the acyl–enzyme intermediate are compared with those previously obtained in the transient (pre-steady state or “burst”) phase. It is found that, while in the transient phase there is no effect of DTAB addition on the kinetic parameters at concentrations below the critical micelle concentration (CMC) of the surfactant, super-activity is observed when the acyl–enzyme intermediate reaches the steady state condition. This difference implies that the surfactant does not modify either the formation or the decomposition of the enzyme–substrate complex (transient phase) but notably increases the rate of disruption of the acyl–enzyme intermediate. 相似文献