Oxygenation and EPR spectral properties of Aplysia myoglobins containing cobaltous porphyrins

Cobalt myoglobins (Aplysia) have been reconstituted from apo-myoglobin (Aplysia) and proto-, meso-, and deutero-cobalt porphyrins. Each of them showed the 30-60 times lower oxygen affinity than those of the corresponding cobalt myoglobins (Sperm whale). Kinetic investigation of their oxygenation by the temperature-jump relaxation technique showed that the low oxygen affinity of cobalt myoglobin (Aplysia) is due to a large dissociation rate constant. The electron paramagnetic resonance (EPR) spectrum of oxy cobalt myoglobin (Aplysia) is affected by the replacement of H₂O with D₂O, suggesting a possible interaction between the bound oxygen and the neighboring hydrogen atom. A low temperature photodissociation study showed that the product of photolysis of oxy cobalt myoglobin (Aplysia) gives an EPR spectrum different from that of the deoxy-cobalt myoglobin (Aplysia) and from that of the photo-lysed form of oxy-cohalt myogloin (Sperm whale). These observations suggest that in oxy-cobalt myoglobin (Aplysia) the bound oxygen might interact with amino acid adjacent to it, but the interaction is weaker than that in oxy cobalt myoglobin (Sperm whale).