Oxy hemerythrin

Figure 6-10 RR spectra of oxy-hemerythrin (excitation at 363.8 nm near O— Fe(III)CT transition). (Reproduced with permission from Ref. 19. Copyright 1986 American Chemical Society.)...

Fig. V-ll. RR spectra of oxy-hemerythrin ( 0, and 02) by 488.0nm excitation, p denotes laser plasma lines...

Holmes MA, Letrong I, Turley S, Sieker LC, Stenkamp RE. 1991. Structures of deoxy and oxy hemerythrin at 2.0 A resolution. JMol Biol 218 583-593. 

Addition of ferricyanide, which oxidizes the pigment to methemery-thrin (Marrian, 1927), also changes the spectrum of a solution of oxy-hemerythrin. However the peak at 330 m/i is common to both forms and the intensities of absorption are quite similar. 

Hemerythrin is a respiratory protein isolated from sipun-culids (marine worms). All sipunculids examined have, in the coelomic fluid, erythrocytes loaded with the protein which in most species so far examined is octameric, but sometimes tri-meric (18, 19) and in one instance dimeric and tetrameric (20, 21). From the retractor muscle of Themiste zostericola, the protein has been characterized as a monomer (22). The monomer (23) and the subunits of the trimer (24) and octamer (25) are remarkably similar in tertiary structure, having a M.W. of about 13,500 daltons. Each subunit contains one binuclear iron site. There is no porphyrin ring and the irons are coordinated only to amino acids, some of which, as well as probably an oxy group, form the binding atoms (26). 

Hemerythrin is the best studied example and high-resolution X-ray data are available for the deoxy (176), oxy (176), met (177), and azido-met (177) forms. Extensive spectroscopic studies have also been carried out on these forms and on the semi-met Fe" Fe form 178). The active site structure of hemerythrin is illustrated in Fig. 40. The two iron atoms are bridged by an oxygen donor (OH or 0 ) and by two carbox-ylates, one aspartate and one gluamate. The remaining protein donors are five histidine residues, three coordinated to one iron and two to the other. In the deoxy form one iron atom is five coordinate and this vacant site can be occupied by dioxygen in oxyhemerythrin or by other... 

Further data on this matter came from the Raman spectrum of oxy( 0 0) hemerythrin, which shows the two oxygen atoms to be in nonctiuiruleni positions. Of the various alternative structures that have been proposed, the Raman data are compatible with only two ... 

The geometry at the iron centres of the bridged dinuclear unit in hemerythrin in its dioxygen-free deoxy (left) and oxygenated oxy (right) forms, with changes upon dioxygen coordination shown. 

The stracture of hemerythrin in a variety of derivatives (oxy, azido, met, and deoxy) is now well-characterized. With three bridging ligands, a distinctive cofacial bioctahedral stereochemistry is seen (Figure... 

Fig. 1 Active site deoxy and oxy forms of the biological oxygen carriers hemoglobin (Hb), hemocyanin (He), and hemerythrin (Hr).

Figure 33. Active site structures of (A) oxy hemeiythriu (PDB code IHMO), (B) deoxy he-merythrin (PDB code IHMD), (C) oxy DcrH-hemerythrin (PDB code 2AWY), and (D) deoxy DcrH-hemerythrin (PDB code 2AWC).

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