Effects of the Tyr64 Substitution on the Stability of Cytochrome c₅₅₃, a low Oxidoreduction‐Potential Cytochrome from Desulfovibrio vulgaris Hildenborough

Cytochrome c553 from sulfate-reducing bacteria is a low-oxidoreduction-potential cytochrome. The primary and tertiary structures show notable differences when compared to mitochondrial cytochromes. Tyr64 replacement in cytochrome c553 provides evidence that this residue is not directly involved in the potential modulation but is mostly implicated in the hydrogen-bond network around the heme. While the different variants obtained did not induce drastic structural modifications, they did affect the stability of the protein. This decrease of stability in acidic and alkaline environments was observed by variations in the optical spectra and by mass spectrometry. In addition, the mobility of aromatic side-chain was found to be increased in the mutant proteins as monitored by two-dimensional NMR spectroscopy.