Single-crystal EPR studies of photolyzed oxy- and nitric oxide-cobalt myoglobins

Publisher Website
Google Scholar
Abstract
Low-temperature photodissociation of oxygen from [sperm whale] oxy-cobalt myoglobin [oxy-CoMb] was studied by single-crystal EPR spectroscopy at 5 K. The photolyzed oxy-CoMb exhibited an EPR spectrum consisting of 2 nonequivalent sets (species I and II) of the principal values and eigenvectors of the g tensors: g1I = 3.55, g2I = 3.47, and g3I = 2.26 for species I, and g1II = 2.04, g2II = 1.93, and g3II = 1.86 for species II, which resembled neither the deoxy nor the oxy form. Possible models of the photodissociated state of oxy-CoMb are proposed by comparison with Co porphyrin complexes. The photolyzed product of nitric oxide-CoMb exhibited new EPR signals at g = 4.3 and a very broad signal at around g = 2. The principal g values were determined from the single-crystal EPR measurements: g1 = 4.39 g2 = 4.27, and g3 = 4.00. Analysis of another EPR signal around g = 2 was difficult due to its broadness. Magnetic interactions were observed. An isotropic EPR signal at g = 4.3 suggested a weakly spin-coupled system between cobaltous spin (S = 1/2 or 3/2) and nitric oxide spin (S = 1/2).