Possible Interaction: Carbon Monoxide and Heme Iron

“ CO binds to the heme iron of most hemoproteins.”

“ CO impedes oxygen supply via haemoglobin by binding with high affinity to heme iron and interferes with enzymes that use heme as prosthetic group.”

“It is well known that CO has a higher affinity for heme iron than does molecular oxygen (O(2)); therefore, CO is potentially toxic.”

“Carbon monoxide CO ) also binds after reduction of the heme iron.”

“Unexpectedly, the binding of CO to heme iron is found to result in a major conformational change at CuB, which now binds only two equidistant histidine imidazoles at 1.95 A and a chloride ion at 2.”

“Remarkably, CO bound to the heme iron is tilted by ~30° with respect to the heme normal, which contrasts to the situation in myoglobin and in present FixLH-CO X-ray crystal structure models.”

“Density-functional calculations demonstrate that indeed vibrational frequency and absorption strength are not linearly coupled and that the absorption strength varies in a slower manner due to charge transfer from the heme iron to CO.”

“Furthermore, stopped-flow kinetics under high pressure show that CO binding to the heme iron is hindered by substrate in NOS, but not in BM3.”

“This suggests a delicate balance between five- and six-coordinate heme iron in both NO and CO complexes.”

“On the other hand, the … recombination of the dissociated CO … heme iron was significantly different between these two forms; the recombination rate constants were 1.1 X 10(3) and 3.… X 10(4) M-1 S-1 at 25 degrees C for the acidic and alkaline forms, respectively.”