FIG. 4.

Amino acid substitutions of Val68 and His97 alters hemin affinity in met(III)Mb. Hemin affinity of met(III)Mb is decreased 39-fold by substitution of the native His⁹⁷(FG3) with alanine. Substitution with Ala97 negates the electrostatic or hydrogen bonding interaction of His97 with the heme-7-propionate, which decreases hemin affinity. Hemin affinity is increased 25-fold by substitution of the native Val⁶⁸(E11) with threonine. Thr68 hydrogen bonds with liganded water in met(III)Mb, which increases hemin affinity since the native Val68 cannot hydrogen bond with the water. The O atom of the threonine side chain hydrogen bonds to the H atom of the water molecule. The PDB structures, 1MYG (47) and 1MNK (69), were used to prepare the images shown using PyMOL software.