Hemoglobin complex with carbon monoxide

Unfortunately, hemoglobin forms a complex with carbon monoxide that is considerably more stable than oxyhemoglobin. The equilibrium constant for the reaction... 

Carbon monoxide is very toxic, rapidly giving a bright red complex with the hemoglobin of blood. Carbon monoxide reacts with alkali metals in liquid ammonia to give the alkali metal carbonyls these white solids contain the [OCCO]2 ion. 

Carbon monoxide is poisonous because it binds to the Fe of hemoglobin more strongly than does oxygen. Hemoglobin complexed with CO cannot carry O2 from the lungs to the tissues. Without O2 in the tissues for metabolism, cells cannot function, so they die. 

Iron, as found in the porphyrin derivative hemoglobin, complexes CO to form a stable metal carbonyl. Iron also forms a variety of metal carbon monoxide derivatives such as the homoleptic Fe(CO)5, Fe2(CO)9 and Fe3(CO)i2, the anionic [Fe(CO)4] and its covalent derivative Fe(CO)4Br2, [CpFe(CO)2] and its alkylated covalent derivatives CpFe(CO)2-R with its readily distinguished n (and and a (and / ) iron carbon bonds. By contrast. Mg in its chlorin derivative chlorophyll, which very much resembles porphyrin, forms no such bonds with CO nor is there a rich magnesium carbonyl chemistry (if indeed, there is any at all). 

Carbon monoxide (CO), a colorless, odorless gas, is responsible for more than half of yearly deaths due to poisoning worldwide. CO has an approximately 250-fold greater affinity for hemoglobin than does oxygen. Consequently, relatively low levels of CO can have substantial and tragic effects. When CO combines with hemoglobin, the complex is referred to as carboxyhe-moglobin, or COHb. 

The first step in the two-step pathway, catalyzed by heme oxygenase (HO), converts heme to biliverdin, a linear (open) tetrapyrrole derivative (Fig. 22-25). The other products of the reaction are free Fe2+ and CO. The Fe2+ is quickly bound by ferritin. Carbon monoxide is a poison that binds to hemoglobin (see Box 5-1), and the production of CO by heme oxygenase ensures that, even in the absence of environmental exposure, about 1% of an individual s heme is complexed with CO. 

Phosphorus trifluoride is a colorless gas, best made by fluorination of PC13 with AsF3 or ZnF2. It forms complexes with transition metals similar to those formed by carbon monoxide. Like CO, it is highly poisonous because of the formation of a hemoglobin complex. Unlike the other trihalides, PF3 is hydrolyzed only slowly by water, but it is attacked by alkalis. 

A pollutant may combine with a cell constituent and form a complex. This often leads to impaired function. For example, carbon monoxide (CO) in the blood readily binds to hemoglobin (Hb), forming carboxyhemoglobin (COHb) as shown below ... 

For example, Jain and Schultz (2) found that hemoglobin/carbon monoxide complexation was favored in a dark environment, while decomplexation was favored in the presence of light. A greater flux of carbon monoxide was achieved through a partially illuminated membrane with darkness upstream and illumination downstream than through totally illuminated or non-illuminated membranes. 

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