Analysis of Heme and Hemoproteins

Heme is perhaps the most ubiquitous cofactor found in nature and the most functionally diverse. Hemoproteins are involved in cell respiration (cytochromes), oxygen-binding and transport (hemoglobin and myoglobin), oxidative bio transformations (cytochrome P-450 and peroxidases), and most recently, as sensors in 2-component regulatory systems (guanylate cyclase, FixL, and CooA). The ability of hemoproteins to carry out extremely diverse reactions arises largely from the protein environment in which the heme molecule resides and specifically the nature of the heme-ligands. Other factors that contribute to the reactivity of the heme are intrinsic to the heme itself, including the substituents on the heme periphery and, in some cases, the covalent attachment of the heme to the protein. The structures of the most common heme-ligands and examples of the hemoproteins in which they occur are found in Table 1 .

Heme coordination	Protein class	Protein function
	Cytochrome b 5	Electron transfer
	Cytochrome c (Class II and IV)
	Cytochrome c oxidase
	(contains heme a)
Hexacoordinate
	Soluble cytochrome b 562	Electron transfer
	Cytochrome c (Class I, IIb and IV)
Hexacoordinate
	Hemoglobin, myoglobin	O 2 -binding
	Fix IVCooA	O 2 /CO-binding
	Soluble guany late cyclase	NO-binding
	Peroxidases	Oxidoreductase
	Heme oxygenase	Oxidoreductase
Hexa/Pentacoordinate
	Catalase	Oxidoreductase
Hexa/Pentacoordinate
	Cytochrome P450	Oxidoreductases
	Nitric oxide synthases
	Chloroperoxidase
Hexa/Pentacoordinate