Active and passive properties of carotid arteries]

A mathematical model of carotid arteries is constructed from the known experimental data. Passive properties of the vascular wall are characterized by an alternating module of elasticity, the active ones by the specific power of muscle contraction. Its maximum value (0,023 n/m-3) is shown to be reached with intravascular pressure 190 mm Hg. The dependence of inner radius on the power of muscle contraction is studied at different values of intravascular pressure. It is shown that theactive properties of carotid arteries are essentially determined by their passive properties and depend on the stretching of the vessel wall.     

Two methods for determination of transketolase activity

Two new optical methods for transketolase activity assay using only one substrate, xylulose 5-phosphate or glycol aldehyde, have been developed. For transketolase activity assay in the first method, it is necessary to add auxiliary enzyme, glyceraldehyde phosphate dehydrogenase. It is not needed in the second method. The range of transketolase concentration in the activity assay is 0.036–0.144 U/ml for the first method and 1.8–6.8 U/ml for the second one. Published in Russian in Biokhimiya, 2006, Vol. 71, No. 5, pp. 693–696.     

The molecular origin of the thiamine diphosphate-induced spectral bands of ThDP-dependent enzymes

New and previously published data on a variety of ThDP-dependent enzymes such as baker's yeast transketolase, yeast pyruvate decarboxylase and pyruvate dehydrogenase from pigeon breast muscle, bovine heart, bovine kidney, Neisseria meningitidis and E. coli show their spectral sensitivity to ThDP binding. Although ThDP-induced spectral changes are different for different enzymes, their universal origin is suggested as being caused by the intrinsic absorption of the pyrimidine ring of ThDP, bound in different tautomeric forms with different enzymes. Non-enzymatic models with pyrimidine-like compounds indicate that the specific protein environment of the aminopyrimidine ring of ThDP determines its tautomeric form and therefore the changeable features of the inducible effect. A polar environment causes the prevalence of the aminopyrimidine tautomeric form (short wavelength region is affected). For stabilization of the iminopyrimidine tautomeric form (both short- and long-wavelength regions are affected) two factors appear essential: (i) a nonpolar environment and (ii) a conservative carboxyl group of a specific glutamate residue interacting with the N1' atom of the aminopyrimidine ring. The two types of optical effect depend in a different way upon the pH, in full accordance with the hypothesis tested. From these studies it is concluded that the inducible optical rotation results from interaction of the aminopyrimidine ring with its asymmetric environment and is defined by the protonation state of N1' and the 4'-nitrogen.