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.

A 119Sn Mössbauer spectroscopic study on the interaction of dimethyltin (IV) derivatives with rat hemoglobin, and of related model systems in aqueous solution.

In the context of a study of the molecular basis of the antileukemia (murine) activity of diorganotin (IV) compounds, the interaction with rat hemoglobin (selected as a model protein) of the representative terms dimethyltin dichloride, dimethyltin glycylglycinate (Me2SnGlyGly), and dimethyltin L-cysteinate (Me2Sn-Cys) has been investigated by 119Sn Mössbauer spectroscopy. In order to possibly determine the reaction pathway, aqueous model systems in Hepes buffer at pH 7.4 were also considered. The structural characteristics of reactants and products were advanced on the basis of semiempirical calculations of Mössbauer nuclear quadrupole splitting parameters, delta E, by the point-charge model approach. In aqueous Hepes at pH 7.4, evidence was obtained for the formation of the five-coordinated species, trigonal bipyramidal type (tbp), Me2Sn(OH)2.Hepes(II), Me2Sn(OH)(GlyGly).Hepes(III), and Me2Sn(OH)Cys(IV) (see Fig. 1). Equatorial groups or atoms would be the Me radicals, as well as OH, N(peptide), and S(thiol), respectively. Hepes would coordinate to tin in axial position through the tertiary amino nitrogen, while cysteine would behave as a bidentate chelating agent, with an axially located amino group. Species (II), (III), and (IV) react with cysteine in aqueous Hepes at pH 7.4, yielding Me2Sn(OH)Cys(IV), as well as Me2SnCys2(V), where tin would be embedded into a tbp structure due to one cysteine probably chelating (equatorial S thiol and axial amino nitrogen), and one monodentate through S thiol. Species (II), (III), and (IV) react analogously with rat hemoglobin, primarily through the S thiol of a cysteine side chain, yielding pellets where the environment of tin could be tetrahedral, such as in Me2Sn(OH)(S thiol), (VI), and tetrahedral (IX) or tbp (V) in Me2Sn(Cys)(S thiol), where Cys would act either as chelating or monodentate. Further reaction of (VI) and (IX) could involve imidazole nitrogen atoms, N het, of histidine side chains, forming tetrahedral Me2Sn(S thiol)(N het), (VIII), or tbp Me2Sn(OH)(S thiol)(N het), (VII), and Me2Sn(Cys)(S thiol)(N het), (V) (see Figs. 1 and 5).