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At least 19 recordsLinked to original sources
PubMed1978

[Chemical modification of lysine epsilon-NH2-groups in horseradish peroxidase. Its effect on enzyme stability. Temperature dependence of thermo-inactivation constants for native and modified peroxidase].

Thermostability of horseradish peroxidase modified by acetic, propionic, butyric, valeric and succinic anhydrides and trinitrobenzolsulfonic acid (TNBS) is studied within the temperature range of 56-80 degrees C. Acylation of 4 amino groups and arylation of 3 amino groups with TNBS are found to stabilize the enzyme, while modification of 6 groups decreases the enzyme stability. Chemical modification of peroxidase does not change its pH-dependence with respect to enzyme thermostability. Thermodynamic activation parameters of irreversible thermoinactivation are determined for native and modified peroxidase. Native peroxidase has deltaH not equal to = 30+/-1 kcal/mole and deltaS not equal to = 14 e. e.; modified by acid anhydrides peroxidase has deltaH not equal to within 64-87 kcal/mole and deltaS not equal to within 110-178 e. e. depending on the nature of a modifying agent. The effect of the structure of a radical introduced into the enzyme molecule, and of a number of modified epsilon-amino groups on thermoinactivation deltaH not equal to and deltaS not equal to values is discussed.

Acylation↗
PubMed1979

Principles of enzyme stabilization. V. The possibility of enzyme selfstabilization under the action of potentially reversible intramolecular cross-linkages of different length.

The denaturing action of guanidine . HCl on modified alpha-chymotrypsin (EC 3.4.21.1) preparations has been studied. The consecutive treatment of alpha-chymotrypsin with N-acetyl-homocysteine thiolactone, 5,5'-dithio-bis-(2-nitrobenzoic acid) and dithiols of HS-(CH2)n-SH type, with n ranging from 4 to 10, leads to enzyme stabilization as a result of protein modification. A greater stabilization effect can be achieved by enriching the protein molecule with groups reactive towards dithiols, after first modifying carboxygroups. In this case dithiol with n=5 forms an intramolecular cross-linkage. If an equimolecular mixture of different dithiols is used for enzyme modification, the enzyme gradually 'selects' 1,5-dithiol for the formation of an intramolecular cross-linkage instead of the initial one-point modification. The use of potentially reversible cross-linkages may be generally employed for the preparation of stabilized water-soluble enzymes via the mechanism of selfstabilization.

Chymotrypsin↗
PubMed1979

Kinetics of digestive enzyme stability in solid state I: application of Weibull distribution function to solid-state enzyme inactivation.

The Weibull distribution function was applied to solid-state enzyme inactivation. On Weibull probability paper (within a narrow range), the plots of the accumulated inactivation ratio of each enzyme versus time regressed to a straight line. The parameters m and k, which correspond to the type and rate of the type and rate of the inactivation, were characteristic of each enzyme. The effect of temperature and parameter reproducibility are discussed.

Drug Stability↗
PubMed1979

The principles of enzyme stabilization. IV. Modification of 'key' functional groups in the tertiary structure of proteins.

The dependence of alpha-chymotrypsin thermostability and catalytic activity on the degree of its amino groups modification has been studied. Modification was carried out by both alkylation (using acrolein with further reduction of Schiff bases by sodium borohydride) and acylation (with siccinic or acetic anhydrides). It has been determined that modification of the majority of titrated amino groups (approximately 80%) only has a slight effect on the first-order rate-constant characterizing the monomolecular process of enzyme thermoinactivation (50 degrees C, pH 8). Thermostability sharply increases (by 120 times) only for a degree of modification higher than 80%, but, nevertheless, the complete substitution of all the titrated amino groups again leads to enzyme destabilization. The conclusion has been drawn that there is only one or two amino groups out out approximately fifteen titrated ones, the modification of which plays a key role in the lateration by the enzyme of its thermostability. The degree of the stabilization effect has been studied relative to both the nature and concentration of the salt added Na2SO4, NaCl, KCl, CCl3COOK, (CH3)4NBr. Ultraviolet absorption (280 nm) of chymotrypsin has also been elucidated with respect to the degree of alkylation of its NH2-groups. The data obtained allowed the conclusion to be drawn that enzyme modification leads to a decrease in the non-electrostatic (hydrophobic) interactions on the surface layer of the globule. As a result, a protein conformation more stable in respect to denaturation (unfolding), is formed.

Acetylation↗
PubMedDate not supplied

[Effect of prosthetic group of horseradish peroxidase on enzyme stability].

Constants of inactivation rate of horseradish peroxidase (HRP) apo-HRP and apo-HRP-protoporphyrin (PP) are estimated at the pH range 2.8-12.8 and 25 degrees C. Two ionogenic groups (acid and alkaline) are detected on cases of HRP and apo-HRP, which are responsible for stable HRP conformation. HRP stability within the pH range 5-10 exceeded 30 times that of apo-HRP, while the stability apo-HRP-PP complex is similar to that of apo-HRP. The data obtained show that formation of complex of apo-HRP with PP, an analogue of the prostetic group lacking central Fe atom, practically does not affect the stability of HRP protein globula at pH 5-10, but significantly stabylized apo-HRP at the extreme pH values. The complex formation of apo-HRP with active prosthetic group - hemin - results on the stable conformation of the HRP protein globula, which suggests a determining role of Fe ion - porphyrin complex (hemin) on the support of the stable HRP structure.

Apoenzymes↗