Cytochrome volume changes

With the enzyme sidechains in fixed positions, the active site volumes computed by the GRID hydrogen probe ranged from 1500 for CYP3A4 to 640 for CYP1A2. With flexible sidechains, the accessible cavity volumes increased from 5% to 10%, probably due to the release of steric hindrance and consequent reduction in steric interaction between the chemical probe and the lateral chains. The explanation put forward is that the cytochromes may use sidechain flexibility to allocate more space when necessary, making sub-pockets or small charmels accessible without changing the structure of the protein backbone. 

The early development of tachypnoea, usually accompanied by hyperpnoea, and resulting in an increased tidal volume, is frequently ascribed to stimulation of the carotid and aortic chemore-ceptors as a result of local accumulation of acid metabolites following cytochrome c oxidase inhibition. However, the general blood acid-base balance changes, notably lactate acidosis, may also be an important factor in breathing changes. 

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