PHYSICOCHEMICAL AND FUNCTIONAL PROPERTIES OF PERINEREIS-CULTRIFERA (GRUBE) ERYTHROCRUORIN

Perinereis erythrocruorin has the following physicochemical properties: , corresponding to a molecular weight around 2.7 · 106; minimum molecular weight (on the basis of the heme content) 23 700 ± 500; isoelectric point 5.1; α-helix content ≈ 40%. At alkaline pH values in the oxygenated form the 55-S molecules dissociate into subunits with a weight average sedimentation coefficient of 3 S, corresponding to a molecular weight ≈ 35 000. Deoxygenation of partially dissociated samples promotes association of the 3-S subunits into a 9 S component. The functional properties of Perinereis erythrocruorin are characterized by a low cooperativity in oxygen binding () 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 of 8