The quaternary structure of Phascolosoma agassizii coelomic hemerythrin

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.

Section: Resultssupporting

confidence: 58%

Moessbauer spectroscopic studies of hemerythrin from Phascolosoma lurco (syn. Phascolosoma Arcuatum)

Clark¹,

Webb²

1981

“…Thus, for example, CD spectra of transition-metal complexes are quite sensitive to the conformational properties of coordinated ligands (Butler and Snow, 1971). Furthermore, small species-specific changes in protein conformation are quite likely, since the hemerythrins do exhibit the following differences in physical properties: (1) hemerythrin from T. dyscritum readily crystallizes from aqueous solutions while the others do not; (2) we have observed different rates for the autoconversion of oxyhemerythrin to methemerythrin between the species; (3) the oligomeric structure of hemerythrin from P. agassizii is a trimer (Liberatore et al, 1974) while the others are octamers; (4) the known amino acid sequences show mutations between and among species (Ferrell and Kitto, 1971;Klippenstein, 1972;Liberatore, 1974);and (5) one of the CD bands in oxyhemerythrin from P. agassizii is red shifted by 10-nm relative to the 336-nm band of the other species. Such species-dependent changes in protein conformation could result in perturbations of ligand orientation or environment at the active site.…”

Section: Discussionmentioning

confidence: 97%

Comparison of hemerythrins from four species of sipunculids by optical absorption, circular dichroism, fluorescence emission, and resonance Raman spectroscopy

Dunn¹,

Addison²,

Bruce³

et al. 1977

Resonance Raman, optical absorption, circular dichroic, and fluorescence emission spectroscopy of hemerythrins from four species of sipunculids (Phascolopsis gouldii, Phascolosoma agassizii, Themiste dyscritium, and Themiste pyroides) reveals no major differences in their active site or tertiary structures. This precludes any change in iron ligands or coodination geometry and makes it unlikely that the active-site structures of P. gouldii and T. dyscritum hemerythrins could be as disparate as indicated by present crystallographic interpretations (Stenkamp, R. E., Sieker, L. C., and Jensen, L. H. (1976), Proc. Natl. Acad. Sci. U.S.A. 73, 349; Klotz, I. M., Klippenstein, G. L., and Hendrickson, W. A. (1976), Science 192, 335). Resonance Raman enhancement profiles of the stretching modes involving coordinated dioxygen maximize with excitation at approximately 525 nm, and correspond to the circular dichroic (CD) transition at approximately 520 nm. For coordinated azide modes in metazidohemerythrins these profiles maximize with excitation at approximately 505 nm corresponding to the 500-nm CD transition. Hemerythrins also possess another resonance Raman peak at approximately 510 cm-1 which show maximum intensity enhancement at approximately 530 nm and this vibration is most likely associated with a permanent iron ligand.

“…As in the case of the hemoglobins and myoglobins, the location and specialized functions of the respective blood and muscle oxygen carriers are reflected in specialized primary structures. However, it is likely that the similarity between T. pyroides and P. gouldii coelomic hemerythrins is not typical since another coelomic hemerythrin, that of the sipunculid Phascolosoma agassizii, is substantially different from these hemerythrins in both quaternary structure (Liberatore et al, 1974) and primary structure (Liberatore, 1974).…”

Section: Discussionmentioning

confidence: 99%

The primary structure of myohemerythrin

Klippenstein¹,

Cote²,

Ludlam³

1976

The complete amino acid sequence of muscle hemerythrin (myohemerythrin) from the sipunculid Themiste (syn. Dendrostomum) pyroides has been determined by analysis of tryptic, chymotryptic, and cyanogen bromide peptides. The primary structure of myohemerythrin differs substantially from that of coelomic hemerythrins of Phascolopsis (syn. Golfingia) gouldii and Themiste pyroides, the amino acid sequence of the muscle protein being only 46 and 45% homologous with the respective coelomic hemerythrins. The most extensive regions of homology between muscle and coelomic proteins occur near the terminii. These and other shorter regions of homology are interpreted in terms of the essential iron ligand residues of the active center.