As a result of reaction of urease with graft copolymer of cellulose and polyglycidyle methacrylate or with carboxymethyl cellulose, products were synthesized, containing about 2% of chemically bound urease. Binding with the cellulose derivatives was accompanied by about two-fold decrease in urease activity. Carboxymethyl cellulose-urease and polyglycidile methacrylate-cellulose-urease might be repeatedly (for 30 cycles) used for hydrolysis of urea; the enzymatic activity of the first compound did not change, but of the second one--was decreased by 30%. Activity of the compounds was not changed after storage within 2 months in 0.1 M phosphate buffer, pH 7.0 at 4 degrees C.

Acrylates↗

PubMedDate not supplied

[Deviations from hyperbolic kinetics in slowly dissociating allosteric enzyme systems].

The feautres of kinetic behavior of dissociating enzyme systems for which the rate of equilibrium between the oligomeric forms is slow in comparison with the rate of the enzymatic process are discussed. It is shown that in slowly dissociating enzyme system of the type Np in equilibrium P (P is the enzyme oligomer, and p is the subunit: N greater than or equal to2) in which P and p forms differ by the character of allosteric interaction between the active and allosteric sites the plots of the initial reaction rate (v) versus substrate (S) or effector (F) concentration may be a very complicated shape. In similar systems the v versus [S]0 plots may have intermediate plateau, maximum and minimum simultaneously, sigmoidality followed by intermediate plateau and so on, and the v versus [F]0 plots may have intermediate plateau.

Allosteric Regulation↗

PubMedDate not supplied

[Kinetic behavior of slowly equilibrating association-dissociation enzyme systems].

The shape of the plots of product accumulation versus time (t) has been analysed for slowly equilibrating association-dissociation enzyme systems of the types 2p in equilibrium P (P is enzyme oligomer which is able to dissociate reversibly forming two identical halves p) and M in equilibrium M2 in equilibrium M2 in equilibrium... (M is monomer which has two association sites overlapping with active sites). It is assumed that the rate of equilibration between oligomeric forms is comparable with the rate of over-all enzymatic reaction and that substrate-oligomer complexes are in rapid equilibrium with free components. It has been shown that characteristic feature of kinetic behavior of slowly equilibrating association-dissociation enzyme systems is that the value of tau depends on enzyme concentration (tau is the intercept on t-axis for linear asymptota of the curve of product concentration versus time at t leads to infinity).

Binding Sites↗

PubMedDate not supplied

[Organotropicity and the dynamics of the clearance of exogenous labelled TSH from the blood under conditions of stimulation and blockade of the thyrotropic function of the hypophysis].

Experiments were conducted on male Wistar rats. Incorporation into the kidney, the liver and the thyroid gland of I131-TSH and its elimination from the blood was studied. The rate of I131-TSH elimination from the blood plasma varied depending on the level of the endogenous TSH in the circulating blood of the recipient rats. The half-elimination period of the I131-TSH from the blood plasma of the intact rats constituted 10.4 minutes. In these animals the labeled hormone accumulated in the thyroid gland only 30 minutes after its administration. In case of an increase of the blood level of endogenous TSH following thyroidectomy the period of half-elimination of the I131-TSH from the plasma fell to 3.6 minutes; with reduction of the endogenous hormone level due to the block of the hypophysial secretion by triiodothyronine the period of the I131-TSH half-elimination rose to 39.4 minutes. In the latter case the labeled hormone failed to be incorporated into the thyroid gland. A conclusion was drawn on a possibility of assessing the level of the thyrotropic activity of the hypophysis on the basis of the changes in the period of the I131-TSH half-elimination from the blood plasma of the recipient animals.

Animals↗