Three-dimensional reconstruction of tubular crystals of catalase

On the basis of electron microscope data the structure of tubular crystals of catalase has been determined with resolution of approximately 25 A. The symmetry of the helical packing of molecules is 142/17. The three-dimensional reconstruction has been carried out in real space. The catalase molecule consists of four subunits whose centers from a fairly flattened tetrahedron. The molecule has dimensions of 69X87X92 A.     

The oxidized (3,3) state of manganese catalase. Comparison of enzymes from Thermus thermophilus and Lactobacillus plantarum.

Manganese catalases contain a binuclear manganese cluster that catalyzes the redox dismutation of hydrogen peroxide, interconverting between dimanganese(II) [(2,2)] and dimanganese(III) [(3,3)] oxidation states during turnover. We have investigated the oxidized (3,3) states of the homologous enzymes from Thermus thermophilus and Lactobacillus plantarum using a combination of optical absorption, CD, MCD, and EPR spectroscopies as sensitive probes of the electronic structure and protein environment for the active site metal clusters. Comparison of results for these two enzymes allows the essential features of the active sites to be recognized and the differences identified. For both enzymes, preparations having the highest catalytic activity have diamagnetic ground states, consistent with the bis-mu-bridging dimanganese core structure that has been defined crystallographically. Oxidative damage and exogenous ligand binding perturb the core structure of LPC, converting the enzyme to a distinct form in which the cluster becomes paramagnetic as a result of altered exchange coupling mediated by the bridging ligands. The TTC cluster does not exhibit this sensitivity to ligand binding, implying a different reactivity for the bridges in that enzyme. A mechanism is proposed involving distinct coordination modes for peroxide substrate in each of the two half-reactions for enzyme turnover.     

The treatment of isolated genera

Problems presented by genera, or small groups of genera, which have been given family rank are reviewed, and the genera are divided into a number of categories according to the closeness of their affinity to other genera or families. Satellite genera that stand in close relation to families should be united with them. Binary families, that have been divided into two (or more) related families, should be re–united. Families connected by linking genera, should, logically, be united but practical considerations usually prevent this. Clusters of diverse but more or less distantly related genera present unusual problems, being treated either as several, often monogeneric families or as a loosely structured family. Truly isolated genera must be given family and often ordinal rank.     

Three-dimensional structure of catalase from Penicillium vitale at 2.0 A resolution

The three-dimensional structure analysis of crystalline fungal catalase from Penicillium vitale has been extended to 2.0 A resolution. The crystals belong to space group P3(1)21, with the unit cell parameters of a = b = 144.4 A and c = 133.8 A. The asymmetric unit contains half a tetrameric molecule of 222 symmetry. Each subunit is a single polypeptide chain of approximately 670 amino acid residues and binds one heme group. The amino acid sequence has been tentatively determined by computer graphics model building (using the FRODO system) and comparison with the known sequence of beef liver catalase. The atomic model has been refined by the Hendrickson & Konnert (1981) restrained least-squares program against 68,000 reflections between 5 A and 2 A resolution. The final R-factor is 0.31 after 24 refinement cycles. The secondary and tertiary structure of the catalase has been analyzed.     

Three-dimensional structure of catalase from Micrococcus lysodeikticus at 1.5 A resolution.

The three-dimensional crystal structure of catalase from Micrococcus lysodeikticus has been solved by multiple isomorphous replacement and refined at 1.5 A resolution. The subunit of the tetrameric molecule of 222 symmetry consists of a single polypeptide chain of about 500 amino acid residues and one haem group. The crystals belong to space group P4(2)2(1)2 with unit cell parameters a = b = 106.7 A, c = 106.3 A, and there is one subunit of the tetramer per asymmetric unit. The amino acid sequence has been tentatively determined by computer graphics model building and comparison with the known three-dimensional structure of beef liver catalase and sequences of several other catalases. The atomic model has been refined by Hendrickson and Konnert's least-squares minimisation against 94,315 reflections between 8 A and 1.5 A. The final model consists of 3,977 non-hydrogen atoms of the protein and haem group, 426 water molecules and one sulphate ion. The secondary and tertiary structures of the bacterial catalase have been analyzed and a comparison with the structure of beef liver catalase has been made.     

Effect of anions and redox state on the activity of manganese containing catalase from Thermus thermophilus

Catalase isolated from thermophilic bacterium Thermus thermophilus (Mn-catalase) is composed of six subunits, each containing binuclear manganese clusters at their active site. The enzyme is active when the metal is in the completely reduced (Mn²⁺---Mn²⁺) state in the pH range 7–10, and loses activity on oxidation. ESR data suggest that the metal turns thereby into the (Mn²⁺---Mn⁴⁺) state. The Mn-catalase activity is inhibited by chloride, nitrate, nitrite, azide, and other singly charged anions, except cyanide. The inhibitory effect of anions increases as the pH value is reduced. The inhibition by hydroxylamine takes place through a lag-phase and is weakly dependent on pH value. The reaction mechanism is discussed in relation with current concepts of catalase reactions of heme-proteins and low-molecular binuclear manganese complexes.