X-ray absorption studies of myoglobin peroxide reveal functional differences between globins and heme enzymes

Abstract

X-ray absorption studies of myoglobin peroxide show that although it is not identical with compound I or II of horseradish peroxidase [Chance, B., Powers, L., Ching, Y., Poulos, T., Yamazaki, I., & Paul, K. G. (1984) Arch. Biochem. Biophys. 235, 596-611], it has some structural features in common with both. As seen in compound I, the Fe-O distance is short, but the iron-pyrrole nitrogen distance is contracted with a longer iron-histidine distance like compound II. The iron has a higher oxidation state than Fe3+, suggesting an oxyferryl ion type species. Comparison of the structures of various peroxidase and myoglobin compounds points out systematic differences that may explain the catalytic activity of the pi cation radical as well as some of the differences between globins and heme enzymes.

Resonance Raman spectroscopy of chloroperoxidase compound II provides direct evidence for the existence of an iron(IV)–hydroxide

“…The extended x-ray absorption fine structure and resonance Raman data reported for these systems are in good agreement with Badger's rule (6,(11)(12)(13)(16)(17)(18)(19), whereas the crystallographically determined bond distances deviate from it substantially (7-9). The long Fe-O bonds that have been reported in the crystal structures of these enzymes appear to be the hallmarks of ferric and ferrous hydroxides (14).…”

“…The long Fe-O bond lengths reported in crystal structures of the ferryl forms of HRP, cytochrome c peroxidase, and myoglobin are at odds with the much shorter (1.64-1.70 Å) oxo-like bond distances obtained from x-ray absorption spectroscopy (11)(12)(13). In hopes of clarifying the issue, we recently examined the applicability of Badger's rule to heme iron-oxygen bonds (14).…”

X-ray absorption spectroscopic characterization of a cytochrome P450 compound II derivative

“…Bond lengths from the EXAFS studies of CYP119 and its derivatives are listed in Table 2, which also contains previously reported EXAFS results for porphyrin-iron-oxo species (17,(36)(37)(38)(39)(40)(41) and heme-thiolate nitrosyl complexes (42). We note that the errors in EXAFS bond lengths typically are 0.01-0.02 Å.…”

“…Conflicting EXAFS results exist for the iron-oxygen bond length in the compound II derivative of horseradish peroxidase, as shown in Table 2 (17,36,39). EXAFS studies of other compound II analogues indicated short iron-oxygen bonds in a model complex (36), in myoglobin peroxide (40), and in cytochrome c peroxidase ES complex (41), each of which has a ferryl-oxo moiety without a porphyrin radical cation. Long iron-oxygen bonds (1.84-1.92 Å) were reported from x-ray crystal structure studies of the compound II derivatives of HRP (43), myoglobin (44), and catalase (45) and also the compound I derivative of cytochrome c peroxidase (46), but Green (47) noted that the x-ray crystal structure results are in conflict with EXAFS, Raman spectral, and computational results and suggested that the long iron-oxygen bonds might have resulted from reduction of the ferryl species to ferric or ferrous species in the x-ray beam.…”

Retracted Article: On the enzymatic activity of catalase: an iron L-edge X-ray absorption study of the active centre

“…3 Contrary to catalase, the reaction of Hb and Mb with peroxide is non-enzymatic, as they are altered through repeated cycles. 4 Structurally, metHb and catalase show major differences. While both have the haem group located at the surface of their monomer units, in Hb, the surface is exposed to the solvent, while in catalase it is positioned inside the tetramer so that relatively long channels lead to the haem moiety.…”