Crystallization and preliminary structural results of catalase from human erythrocytes

Catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase, E.C. 1.11.1.6 ) is present in most aerobic prokaryotic and eukaryotic cells. Despite a la rge number of studies on catalases, the only mammalian catalase structure a vailable is that from beef liver, in which about 50% of the haem groups are degraded to bile pigments. Three different crystal forms of human erythroc yte catalase were obtained by the hanging-drop vapour-diffusion technique u sing PEG as precipitant. Monoclinic crystals, with space group PZ, and unit -cell parameters a = 102.9, b = 140.0, c = 173.6 Angstrom and beta = 103.2 degrees, require NADP(H) in the crystallization solution. Two types of hexa gonal packing, with unit-cell parameters of either a = b = 86.9, c = 255.5 Angstrom or a = b = 90.0, c = 521.2 Angstrom, were obtained under identical crystallization conditions in the absence of NADP(H). Only one diffraction data set could be collected: this was obtained from the hexagonal crystals with the smaller c axis using synchrotron radiation, with resolution to 2. 65 Angstrom. A molecular-replacement solution, determined using a modified beef-liver catalase model as a search structure, corresponds to space group P6(4)22 and contains a single subunit in the asymmetric unit, with an esti mated solvent volume of about 50%. The packing determined suggests how mino r rearrangements might allow the transition between both hexagonal crystal forms and provides an explanation for the anisotropic character of the corr esponding diffractions.