Spin-labeled analogues of vitamin B6: 2, 2, 6, 6-tetramethyl-N-oxylpiperydinyl-4-(5' phosphopyridoxyl)-amine (1) and 2, 2, 6, 6-tetramethyl-N-oxyl-piperydinyl-4-(pyridoxal-5')-phosphate (II) are synthesized. There analogues were shown to interact in the equimolar ratio with the active site of cytosol aspartate transaminase. It was proved by CD-titration of apotransaminase with I and II and by competition between the coenzyme and synthesized analogues. The free valency of spin-labeled coenzymes immediately disappears after interaction with the apoenzyme due to iminoxyl group reduction. The binding of I and II with the apoenzyme is accompanied by oxidation of one of the inner cysteine residues. The reactivation of the modified apoenzyme with PLP is not less than 65% of original transaminase activity. The analysis of space-filling atomic models of synthesized compounds allows to conclude that the distance between the centre of pyridine ring of the coenzyme and the modified thiol group is not more than 8 A.

Apoproteins↗

PubMedDate not supplied

[Polarity of the environment as a factor determining DNA conformation].

Polarity of double and ternary water-nonelectrolyte systems at the component ratio, corresponding to a half-transition point of DNA from B to A form was evaluated from ESR spectra of a spin-probe. In all cases examined the isotropic super-fine splitting constant (aN) is the same with an accuracy of 0.05 gauss. Small differences in aN are well correlated with the concentration of the groups which are able to form hydrogen bonds with the nitroxide fragment of the radical. Thus, media polarity is a factor which determines the A--B equilibrium of DNA in solution.

Chemical Phenomena↗

PubMedDate not supplied

[Macromolecule rotative correlation time measurement by ESR for covalently bound spin label].

The dependence from temperature and viscosity of the shifts of the internal and external wide extremums in the ESR spectra of spin labelled bovine serum albumin has been studied. 2,2,6,6-tetramethylpiperidine-NI-oxyl-4-iodacetamide was used as a spin label. The obtained dependences was shown to be a consequence of the label participation in two types of rotations: an anisotropic fast rotation with tau less than 10(-9) sec relatively to a macromolecule, and the isotropic one with tau greater than 10(-8) sec due to rotation of the macromolecule itself. These conclusions were done on the basis of a model for complex rotation of the spin label. Comparison of theoretical and experimental data makes it possible to determined the correlation time for the protein moiety, to evaluate quantitatively the polarity of surroundings of the iminoxyl and to introduce a numerical parameter for the degree of mobility of the spin label relatively to protein molecule.

Electron Spin Resonance Spectroscopy↗