[Quaternary structure of histidine decarboxylase according to small-angle x-ray diffraction and electron microscopic findings]. / Chetvertichnaia struktura gistidindekarboksilazy po dannym rentgenovskogo malouglovogo rasseianiia i élektronnoi mikroskopii.

The data on small angle X-ray scattering with histidine decarboxilase (HDC) from Micrococcus sp. n. were analysed and a line of succesively improving approximations of the molecule shape was found: by oblate ellipsoid a:b:c = 1:10.63, by continuous cylinder and hollow cylinder with H = 50 A, 2R = 76 A, 2r = 8A. Biochemical data and electron micrographs of HDC obtained made possible to distinguish subunits and thus to increase resolution of the model. The model of the enzyme molecule consisting of three subunits is suggested, whose X-ray small angle scattering curve well agrees with the experimental one up to value S = 0.21 A-1.

[Determination of the molecular weight and form of the molecule histidine decarboxylase by the method of small-angle x-ray scattering]. / Opredelenie molekuliarnogo vesa i formy molekuly gistidin-dekarboksilazy metodom rentgenovskogo malouglovogo rasseianiia.

Shape and molecular weight of histidine-decarboxylase from Micrococus sp. n. were studied by the method of X-ray small-angle scattering. The inertion radius of the molecule: Rg-2,93 nm. The shape of the molecule is adequately approximated by rotation ellipsoids of two possible variants: the elongated and flattened ones. The eccentricity in both cases is 1.6. The volume of the enzyme molecule V=190 nm3. The molecular weight of histidine-dexarboxilase obtained from the X-ray experiment M=102 000 c.u.

[Study of the structure of the histidine decarboxylase of Micrococcus sp. n. by the method of circular dichroism]. / Izuchenie struktury gistidindekarboksilazy Micrococcus sp. n. metodom kruglovogo dikhroizma

Ring dichroism spectra (RD) of histidine decarboxylase (HDC) from Micrococcus sp. n. at the regions of peptide bonds (200-240 nm) and aromatic amino acids (250-300 nm) absorption are studied. The treatment of RD spectra according to methods of Greenfield-Fasman, Saksena-Vetlaufer and Mayer permits to conclude that at the pH range within 4-8 the content of ordered structures of alpha-helix type comprises 20%, that of beta-structure type-40%, while the rest 40% are represented with polypeptide chain in a disordered globular state. When pH is varied from 1 to 12, the content of alpha-helices decreases from 17 to 5%. There are two distinct dichroic bands in the spectrum of aromatic chromophores absorption (at 270 and 290 nm), the former containing tirosine, tryptophane and phenylalanine residues and the latter being induced with triptophane residues. The study of HDC RD spectra at the regions of peptide bonds and aromatic acids absorption at different temperatures has shown that a part of triptophane, tyrosine and phenylalanine residues is in an ordered structure of the alpha-helix type. The HDC undergoes irreversible changes under heating to 70 degrees and in 8 M urea. 5 M guanidine chloride eliminates the ordered HDC structure, while sodium dodecylsulphate at concentrations up to 1% does not affect the enzyme structure.

[Flourescent properties of histidine decarboxylase from Micrococcus sp. n]. / Flourestsentnye sovistva gistidindekarboksilazy Micrococcus sp. n

A dependency of fluorescence parameters of histidinedecarboxylase (HDC) from Micrococcuc sp. n. on pH values is studied. Native HDS has a short-waved maximum position (325 nm) and a small half-width of the fluorescence spectrum (48nm). The change in the quantum yield of the enzyme fluorescence was parallel with the change of the enzymatic activity. Triptophane residues of native HDC are located at hydrophobic region of the enzyme globula. The dependency of HDC flourescence parameters on pH values in 8 M urea was similar to that of free triptophane. A comparative study of fluorescences parameters of HDC and its inhibitory complexes with methyl ester of histidine (MEH), hydroxylamine and p-chloromercuriumbensoate is carried out. The effect of HDC interacting with inhibitors on fluorescence parameters of the enzyme is discussed. No differences were found in infra-red spectra of HDC and its inhibitory complex with MEH.

[Specific modification of free lysine amino groups of histidine decarboxylase from Micrococcus sp. n. by trinitrobenzene sulfonic acid]. / Spetsificheskaia modifikatsiia svobodnykh aminogrupp lizina gistidindekarboksilazy iz Micrococcus sp. n. trinitrobenzolsul'fokislotoi

It has been found that 14 lysine residues are accessible for trinitrobenzene sulfonic acid (TNBS) in the molecule of histidine decarboxylase (HDC). The other 62 lysine residues in the molecule of native HDC are masked and inaccessible for TNBS. It is demonstrated that the SH- and alpha-amino groups of methionine are not modified by TNBS. A correlation between the decarboxylase activity of the enzyme and the degree of its trinitrophenylation has been studied. HDC, whose molecule contains 3--9 TNP groups, retains up to 90--97% of its initial activity. Trinitrophenylation of 14 lysine residues induces inactivation of HDC by 33--34%, which probably depends on conformational changes or steric hindrances, occurring in the catalytic site of the modified active centre of HDC. Using circular dichroism and fluorescence methods as well as disc-electrophoresis in polyacrylamide gel, it has been shown that trinitrophenylation does not cause any significant changes in the enzyme structure. The TNP groups have been found to be localized in the large and small subunits of the HDC molecule.