ABSTRACT
The three-dimensional structure of the heme-containing fungal catalase from Penicillium vitale (m.m. 2,80,000) has been studied by X-ray analysis at 2·0 A resolution. The molecule is tetramer, each subunit contains 670 aminoacid residues identified to construct “X-ray” primary structure. The subunit is built of three compact domains and their connections. The first domain of about 350 residues contains a β-barrel flanked by helices, the second domain of 70 residues is formed by four helices and the third one is composed of 150 residues and is topologically similar to flavodoxin. The active site including heme is deeply buried near the β-barrel. A comparison of the structure of catalase from Penicillium vitale with that of beef liver catalase revealed very close structural homology of the first and the second domain, but the third domain is entirely absent in beef liver catalase. A catalase from thermophillic bacteria Thermus thermophilus (m.m. 2,10,000) has been first isolated, crystallized and studied by X-ray analysis. Crystals are cubic, space group is P213, a = 133·4 Å. The molecule is a hexamer with trigonal symmetry 32. The electron density map at 3 Å resolution made it possible to trace the polypeptide chain. The main structural motif is formed by four near parallel helices. There is no heme in Thermus thermophilus catalase, the active site is between the four helices and contains two manganese ions.