Physicochemical and functional properties of Perinereis cultrifera (Grübe) erythrocruorin.
Perinereis erythrocruorin has the following physicochemical properties: So20,w = 55S, corresponding to a molecular weight around 2.7-10(6); minimum molecular weight (on the basis of the heme content) 23 700 +/- 500; isoelectric point 5.1; alpha-helix content approximately 40%. At alkaline pH values in the oxygenated form the 55-S molecules dissociate into subunits with a weight average sedimentation coefficient of 3S, corresponding to a molecular weight approximately 35 000. Deoxygenation of partially dissociated samples promotes association of the 3-S subunits into a 9S component. The functional properties of Perinereis erythrocruorin are characterized by a low cooperativity in oxygen binding (n 1/2 = 1.5) at neutral pH. Cooperativity increases reversibly towards both the acid and alkaline pH range, irrespective of changes in molecular weight. This finding, taken together with the ultracentrifuge results, suggests that a subunit may represent the functional unit of the protein. The pH dependence of the oxygen affinity can be accounted for in terms of a single oxygen linked group with a pK of 8.
D000495:Allosteric Site; D000845:Annelida; D002248:Carbon Monoxide / Q000378:metabolism; D002413:Cations, Divalent; D002942:Circular Dichroism; D004902:Erythrocruorins / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D010100:Oxygen / Q000378:metabolism; D013057:Spectrum Analysis; D014461:Ultracentrifugation
D002413:Cations, Divalent; D004902:Erythrocruorins; D006454:Hemoglobins; D002248:Carbon Monoxide; D010100:Oxygen