| The heme-containing active site of catalases is buried in the core of the protein. The flow of substrate and product to and from the site takes place through a network of channels that extend from the molecular surface to the core of the protein. Three channels have been identified in catalases, two of which have been characterized: the main channel and the lateral channel. The main channel with length of 55 A in catalase HPII approaches the distal side of the heme perpendicular to its plane. The lateral channel with length of 30 A extends from molecular surface to a cavity where it bifurcates before reaching the active site in the plane of the heme. This study investigates the role of the lateral channel by changing key residues in the heme pocket and the lateral channel using site directed mutagenesis. The targeted residues were isoleucine 274 in the entrance to the lateral channel, phenylalanine 206 and phenylalanine 214, close to the heme, and glutamate 270 about 15 A up the lateral channel. (Abstract shortened by UMI.)... |
