Porphyrin π-stacking in a heme protein scaffold tunes gas ligand affinity

A phenylalanine-porphyrin off-set π-stack was found to exert significant effects on ligand binding properties of Tt H-NOX, without changing the protein structure. Removal of the π-stack resulted in a modest change (~ 40 mV) in midpoint potential and an order of magnitude change in O2 affinity.