Reaction of Aplysia limacina metmyoglobin with hydrogen peroxide.

Myoglobin (Mb) from gastropod mollusc Aplysia limacina shows only 20% sequence homology to the 'prototype' sperm whale Mb but exhibits a typical Mb fold and can reversibly bind oxygen. An intriguing feature of aplysia Mb is that it lacks the distal histidine and displays a ligand stabilisation based on an arginine. Here we report the reaction of aplysia metMb with hydrogen peroxide studied by optical and electron paramagnetic resonance (EPR) spectroscopies.

On the formation, nature, stability and biological relevance of the primary reaction intermediates of myoglobins with hydrogen peroxide.

The reaction between hydrogen peroxide and myoglobin (or haemoglobin) ferric haem is a two-electron redox process, yet the stable product is ferryl haem, retaining only one oxidizing equivalent. We have used SVD (singular value decomposition) and global spectroscopic analysis to examine the transient primary spectral intermediates in this reaction, which have been reported as either "compound 0"(ferric peroxide) or "compound I"(ferryl and porphyrin cation radical) types and which may precede the formation of ferrylmyoglobin. To test the hypothesis that the distal histidine facilitates ferryl formation we studied the myoglobin-like haemoglobin from the gastropod mollusc Aplysia fasciata, where this histidine is replaced by valine and its hydrogen bonding role is taken up by a non-homologous arginine.