Hemoglobin the iron gets recycled. This process also produces one molecule of carbon monoxide for every molecule of heme degraded. Heme degradation is one of the few natural sources of carbon monoxide in the human body, and is responsible for the normal blood levels of carbon monoxide even in people breathing pure air. The other major final product of heme degradation is bilirubin. Increased levels of this chemical are detected in the blood if red blood cells are being destroyed more rapidly than usual. Improperly degraded hemoglobin protein or hemoglobin that has been released from the blood cells too rapidly can
Fetal hemoglobin blood cells, this substance decreases the affinity of hemoglobin for oxygen. 2,3-BPG is also present in fetal red blood cells, but interacts less efficiently with fetal hemoglobin than adult hemoglobin. This is due to a change in a single amino acid (residue 143) found in the 2,3-BPG 'binding pocket': from histidine to serine, which gives rise to the greater oxygen affinity. Whereas histidine is positively charged and interacts well with the negative charges found on the surface of 2,3-BPG, Serine has a neutrally charged side chain at physiological pH, and interacts less well. This change results in less binding of