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Research on the heme coordination environment and ligand binding properties of ferrous bovine soluble guanylyl cyclase (Fe(II)sGC) and Fe(II)sGC(CO) reveals the axial liganding of histidine in Fe(II)sGC and the failure of CO to activate the enzyme. CO fails to activate the enzyme even though it binds to Fe(II)sGC hexacoordinately. Activation of sGC by nitric oxide can be made possible by breaking the bond between heme iron and histidine.

The results of intermolecular, intramolecular and intrasubstituent kinetic deuterium isotope effect studies on secondary amine monooxygenase-catalyzed C-H bond cleavage during oxidative N-demethylations are reported. This catalysis appears to proceed through a deprotonation limiting mechanism, similar to that employed by cytochrome P-450, the only other heme-containing monooxygenase.

Bis-His ligation of heme iron is caused by the replacement of Phe82 by His in the iso-1-cytochrome c mutant obtained from the yeast Saccharomyces cerevisiae. Occurrence of heme iron ligation is indicated by electron paramagnetic resonance spectroscopy and near-infrared circular dichroism. The ligation occurs since the His on the heme's distal sides is His82. Distal ligand ligation produces variation in the structure of co-ordination.