Resonance Raman Spectra of Extracellular Ligninase: Evidence for a Heme Active Site Similar to Those of Peroxidases

The first resonance Raman spectra of the heme active site of the lignin-degrading enzyme ligninase are described. The strong correspondence between the spectra of ligninase and those of animal and plant peroxidases indicates that the local heme environment of ligninase greatly resembles those of peroxidases. By analogy with other heme-containing proteins it is likely that both the ferric and ferrous forms of ligninase are five-coordinate and high spin. The addition of cyanide to ferriligninase results in the formation of a low-spin six-coordinate heme active site. An iron-histidine stretching mode at ~244 cm-1 is suggested for ferroligninase in analogy with those of other peroxidases.