The Conformer Nature of the Multiple Forms of Beef Liver Catalase as Obtained by Biochemical and Small-Angle X-Ray Scattering Experiments. A Model for the Quaternary Structure of the Beef Liver Catalase Molecule

Abstract

Two of the five multiple forms of beef liver catalase have been extensively studied using biochemical and biophysical analysis techniques. The two molecules, cat I and cat V, have different isoelectric points (pH 6.55 and 5.6), different surface charges (25.8 and 32.7 elementary charges) and display different numbers of primary amino groups on their surfaces. The numbers of tyrosine residues on the surfaces of the two molecules are also different (16 and 10 at pH 10). Since the two forms of catalase can be interconverted, the described changes may be caused by conformational changes of the four protein subunits within the molecule. This mobility of the polypeptide chains is also demonstrated by the different absorption spectra below 390 nm. Using small-angle X-ray scattering, the radii and the volumes of the two catalase forms were shown to be different (cat 1 is smaller than cat V). All five multiple forms of beef liver catalase are concormers of the molecule. A model for the quaternary sturcture of the beef liver catalase are conformers of the molecule. A model for the quaternary structure of the beef liver catalase molecule is suggested. It consists of a regular configuration of four prolate rotational ellipsoids (semiaxes: a = 52 A, b = c = 21 A) in close contact in which the nearest neighbour subunits are shifted by 37 A parallel to each other. Thus the height of the complete molecule is 141 A and the diameter 94 A.