CATALASE OF NEUROSPORA-CRASSA .2. ELECTRON-PARAMAGNETIC RESONANCE AND CHEMICAL PROPERTIES OF THE PROSTHETIC GROUP

The inducible catalase from Neurospora crassa 5297a when examined at 13 K exhibits electron paramagnetic resonance (9 and 34 GHz) with two sets of principal features at g = 6.33, 5.48, and 1.99 and 6.62, 5.18, and 1.99. Minor amounts of other resonances are seen near g = 6. Sodium formate converts these to a single species with features at g = 6.51, 5.34, and 1.99. This is consistent with the presence of two or more high-spin ferric porphyrin complexes in the untreated enzyme. The azide complex of this catalase yielded a single well-defined set of resonances at g = 2.50, 2.26, and 1.87, indicating that the high-spin forms of the enzyme are converted to a single low-spin compound under these circumstances. Integration of this signal indicated that at least 90% of the heme iron in the native enzyme is present as high-spin ferric complexes. In some preparations of the untreated enzyme small amplitude resonances at g = 2.42, 2.30, and 1.89 were observed; these appear to arise from inactive forms of the enzyme. Extraction of the heme group and subsequent removal of iron and conversion to the methyl ester yield a porphin with absorbance maxima at 653, 599, 533, 500, and 399 nm in a ratio of 2.92:0.33:0.33:1.00:12.9. The spectrum closely resembles that of the chlorin prepared by J. Barrett [(1956) Biochem. J. 64, 626] from cytochrome a2 of Escherichia coli and is distinct from any reported porphyrin spectrum. The chromatographic properties of the catalase chlorin suggest the presence of approximately four carboxyl groups, whereas chlorin a2 is reported to have two carboxyl groups. We were unable to reoxidize the presumed chlorin to a porphyrin by using 2, 3-dichloro-5, 6-dicyano-benzoquinone, a phenomenon observed previously with ste-rically hindered chlorins and phorbins [Woodward, R. B. (1961) Pure Appl. Chem. 2, 383], Nonetheless, the evidence presented strongly suggests that, unlike previously studied catalases, the inducible catalase of N. crassa has as its prosthetic group a polar high-spin ferric dihydroporphyrin complex. © 1979, American Chemical Society. All rights reserved.