[Quaternary structure of histidine decarboxylase according to small-angle x-ray diffraction and electron microscopic...

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.