<unk> s are generally membrane-bound hemoproteins that contain heme groups and carry out electron transport.
They are either found as monomeric proteins (i.e.<unk>  c) or as subunits of bigger enzymatic complexes that catalyze redox reactions.  They are found in the mitochondrial inner membrane and endoplasmic reticulum of eukaryotes, in the chloroplasts of plants, in photosynthetic microorganisms, and in bacteria.
Cytochrome
Chlorophyll
Phosphocreatine
Coenzyme
Methaemoglobin
Hydroquinone
Flavin
Nicotinamide adenine dinucleotide phosphate