Cytochromes c′ are bacterial heme proteins with a vacant distal coordination site available for binding diatomic gases. Distal heme ligation is sterically hindered by a non-polar residue (typically Leu, Phe, or Met). In the case of Alcaligenes xylosoxidans cytochrome c′ (AXCP), distal steric hindrance is proposed to cause the conversion of the six-coordinate heme-NO complex (6cNO) to a five-coordinate heme-NO complex (5cNO) on the opposite (proximal) heme face. By contrast, the NO complex of Rhodopseudomonas Palustris (RPCP) exists as a mixture of 6cNO and 5cNO species. Here, we have explored the role of steric hindrance in controlling RPCP reactivity with diatomic gases (NO, CO, O2) using resonance Raman spectroscopy and time-resolved UV-vis absorption.

Molecular recognition of diatomic gases in Rhodopseudomonas Palustris Cytochrome c′

249th National Meeting (2015)

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