Hemerythrin, absorption spectrum

Controlled reaction of G. gouldii hemerythrin with tetranitromethane has shown that tyrosyl residues 8 and 109 and, to a lesser extent, tyrosyl 67 are protected from nitration in the iron-protein (201—202). The more readily nitrated residues, namely tyrosines 18 and 70 are, hence, likely to he on the surface of the monomer. This partial modification did not affect either iron-binding, as judged by its visible absorption spectrum,... 

Early authors attempted unsuccessfully to find bands characteristic of hemoglobin in the absorption spectrum of hemerythrin. Deoxygenated hemerythrin shows no specific absorption bands in the region between 300 and 600 m/i. Oxyhemerythrin has a strong band in the visible region with a peak at 500 m/i and even more intense absorption in the near ultraviolet region with a peak at 335 m/x and a shoulder at about... 

The diiron center of nigerythrin has been studied by absorption and EPR spectroscopy [414], The low-temperature EPR spectrum showed three resonances at g < 2 (gav = 1-74), consistent with two antiferromagnetically coupled irons (Fe " with S = 5/2 and Fe with S = 2), yielding an Stat = V2 spin ground state. The spectram is reminiscent of those observed for mixed-valent MMO ( 2) and hemerythrin ( 8) [80,81]. EPR spectroscopy was also used to determine the redox potentials of the non-heme diiron center and the mononuclear iron of the FeS4 site in nigerythrin, which were found to be > -1-200 mV. 

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. 

---