Allosteric transition in triply met-haemoglobin

• Published in: Journal of molecular biology Vol. 217; no. 2; pp. 303 - 306
• Main Authors: Marden, Michael C., Kister, Jean, Bohn, Brigitte, Poyart, Claude
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 20.01.1991; Elsevier
• Subjects: Allosteric Regulation; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Carbon Monoxide - chemistry; Fundamental and applied biological sciences. Psychology; Heme - chemistry; hemoglobin; Hemoproteins; Humans; In Vitro Techniques; inositol hexakisphosphate; Metalloproteins; Methemoglobin - ultrastructure; Oxidation-Reduction; Oxygen - chemistry; Phytic Acid - chemistry; Proteins; Structure-Activity Relationship; IHP; Hb; L345; OEC; Ligand binding; Hemoprotein; Oxygen; Allosteric transition; PH; Methemoglobin; Oxidation; Carbon monoxide; Kinetics; Inositol phosphate; Photodissociation
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(91)90544-G

Methaemoglobin undergoes a transition to a T-like form at acid pH in the presence of strong effectors such as inositol hexakisphosphate (IHP), as evidenced by spectroscopic and oxidation potential measurements. Since oxygen and CO do not bind to the ferric haems, it is difficult to compare the properties of the R-met and T-met forms with those of ferrous haemoglobin. We have therefore prepared 90% oxidized samples, where the dominant signal for ligand (oxygen or CO) binding is due to tetramers with three met haems. Measurements were made of the oxygen equilibrium curves and CO rebinding kinetics after photodissociation. Without effectors, the partially oxidized samples show mainly R-state properties. Addition of IHP at acid pH induces an increase in T-state behaviour, as indicated by a lower oxygen affinity and a higher fraction of the slow bimolecular component for CO rebinding.