THE THREE-DIMENSIONAL STRUCTURE OF BEEF LIVER CATALASE AT 2.5 ANGSTROMS RESOLUTION
Abstract
The Problem. Peroxidases, a subset of heme containing proteins, differ in structure and function. The catalytic intermediate of all peroxidases (Compound I), formed from the reaction of enzyme with hydrogen peroxide, oxidizes a substrate molecule. CcP('+) is a special peroxidase in that the substrate of the oxidized enzyme is cytochrome c. However, catalase and horseradish peroxidase, among other peroxidases, oxidize a variety of substrates. In addition, the catalase Compound I can oxidize a hydrogen peroxide. To improve our understanding of hemoprotein chemistry, the three-dimensional sturcture of catalase was investigated. The Results. The structure of catalase (E.C. 1.11.1.6 hydrogen peroxide:hydrogen peroxide oxidoreductase) from beef liver has been determined to 2.5 (ANGSTROM) resolution with the isomorphous and molecular replacement methods. Five data sets were collected from the trigonal (P3(,2)21) crystal form with half of the tetramer in the crystallographic asymmetric unit. The oscillation method was used. The orientation of the noncrystallographic molecular two-fold axes was determined with the rotation function. This information was used to locate the heavy atom positions in one derivative from a difference Patterson map using a vector search method. Heavy atom positions of other derivatives were located with difference Fourier techniques. Heavy atom parameters were refined to 2.7 (ANGSTROM) resolutions. The position of the molecule center and the orientation of the noncrystallographic diad were accurately estimated by examining the agreement between electron density at noncrystallographically related grid points. The electron density was improved by averaging about the noncrystallographic two-fold axis. The catalase tetramer id dumbbell shaped with a waist in the P = 0 plane. Each subunit contans 26% helix and 12% beta structure, and consists of four distinct structural domains. Intersubunit contacts form the basis for an examination of tetramer assembly. The heme is well buried, about 20 (ANGSTROM) below the molecular surface and is accessible only through a 30 (ANGSTROM) long hydrophobic channel. The heme environment is essentially hydrophobic. The distal coordination site is empty. The proximal coordination site is occupied by the phenoxy oxygen of Tyr 357. The spectral, magnetic, and chemical properties are considered in light of the unique heme environment of catalase.
Degree
Ph.D.
Subject Area
Biochemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.