Membrane-bound cytochrome-containing enzyme complexes can now be isolated from membrane fragments in a “solubilized state". These solubilized components can then be further purified by conventional biochemical techniques. Bacterial electron transport systems are quite complex and diverse with respect to the types of electron carriers found within their membranes. Cytochrome o is a carbon-monoxide-binding hemoprotein that is found primarily in bacterial electron transport particles. Cytochrome oxidases function as terminal oxidases which are membrane-bound enzyme complexes that utilize molecular oxygen as a terminal electron acceptor for bioenergetic processes like oxidative phorphorylation. Mixed-function oxidases are multienzyme complexes, which possess oxygen-reactive hemoproteins that will use an electron transport carrier system to energize or activate molecular oxygen so that while one atom of oxygen serves as an electron acceptor. S. K. Erikson and H. Diehl, using action spectra studies, reinvestigated the respiratory electron transport chain of Azotobacter vinelandii.