Mössbauer spectroscopic studies of hemerythrin from Phascolosoma lurco (syn. Phascolosoma arcuatum).

Hemerythrin from coelomic cells of Phascolosoma lurco (syn. P. arcuatum) was isolated by gel filtration as two components, hemerythrin-I (25%) and hemerythrin-II (75%). The Mössbauer spectrum of oxyhemerythrin-II consisted of two pairs of lines of the same isomer shift (0.5 mm s(-1) corresponding to Fe(III) but different quadrupole splitting (1.01 and 2.02 mm s(-1). Application of a 2.5-T magnetic field at 4.2 K caused no significant spectral broadening. The 2FE.O2 binding site thus contains two nonequivalent high-spin Fe(III) ions that are antiferromagnetically coupled. The Mössbauer spectra of the minor component, hemerythrin-I, indicated an identical binding site. On deoxygenation, the spectrum was dominated by a simple quadrupole split doublet corresponding to Fe(II), indicating that the binding site in this derivative contains two identical Fe(II) ions that interact only weakly, if at all. The Mössbauer spectra of azidohemerythrin-II indicated that this derivative also contains a pair of antiferromagnetically coupled Fe(III) ions with the same isomer shift (0.5 mm s(-1)) but quadrupole splittings (1.40 and 1.96 mm s(-1)) that are not identical with those in oxyhemerythrin.