| Popis: |
The pH dependences of the electronic absorption spectra of deoxy and nitrosyl erythrocruorin, isolated from Arenicola marina, are reported. The optical transitions have pKa values of 10.8 and 10.2, respectively. By comparing titrations of the protein at pH 7.0 with imidazole and with SDS, we conclude that the optical transition observed for the deoxy derivative at high pH values is due to the coordination of an imidazole group to the central iron atom. Titrations of the deoxy protein, in its protonated and deprotonated forms with NO are also reported. These results are discussed in terms of structural rearrangements around the protohaem IX group, which are linked to more general protein conformational changes and to changes in the quarternary structure, as monitored by determinations of S20 values for the deoxy and NO derivatives at a number of pH values. |
