TY - JOUR
T1 - Mechanisms of autoxidation of the oxygen sensor FixL and Aplysia myoglobin
T2 - Implications for oxygen-binding heme proteins
AU - Gonzalez, Gonzalo
AU - Gilles-Gonzalez, Marie A.
AU - Rybak-Akimova, Elena V.
AU - Buchalova, Maria
AU - Busch, Daryle H.
PY - 1998/7/14
Y1 - 1998/7/14
N2 - On exposure to oxygen, ferrous heme is thought to autoxidize via three distinct mechanisms: (i) dissociation of protonated superoxide from oxyheme; (ii) reaction between a noncoordinated oxygen molecule and pentacoordinate deoxyheme, and (iii) reaction between a noncoordinated oxygen molecule and an intermediate having water coordinated to the ferrous heme iron. The formation of a hexacoordinate aquomet (H2O·Fe3+) species has been proposed to drive mechanism (iii); consequently, heme proteins with a pentacoordinate met (Fe3+) form might be expected to lack this pathway. We have measured the dependence of autoxidation rate on oxygen concentration for Rhizobium meliloti FixL and Aplysia kurodai myoglobin, which have pentacoordinate met forms. For both proteins, the bell shape of this dependence shows that they autoxidize primarily by mechanism (iii), indicating that a hexacoordinate aquomet species is not required for this mechanism. A novel presentation of the oxygen dependence of autoxidation rates that uses heme saturation, rather than oxygen concentration, more clearly reveals the relative contributions of autoxidation pathways.
AB - On exposure to oxygen, ferrous heme is thought to autoxidize via three distinct mechanisms: (i) dissociation of protonated superoxide from oxyheme; (ii) reaction between a noncoordinated oxygen molecule and pentacoordinate deoxyheme, and (iii) reaction between a noncoordinated oxygen molecule and an intermediate having water coordinated to the ferrous heme iron. The formation of a hexacoordinate aquomet (H2O·Fe3+) species has been proposed to drive mechanism (iii); consequently, heme proteins with a pentacoordinate met (Fe3+) form might be expected to lack this pathway. We have measured the dependence of autoxidation rate on oxygen concentration for Rhizobium meliloti FixL and Aplysia kurodai myoglobin, which have pentacoordinate met forms. For both proteins, the bell shape of this dependence shows that they autoxidize primarily by mechanism (iii), indicating that a hexacoordinate aquomet species is not required for this mechanism. A novel presentation of the oxygen dependence of autoxidation rates that uses heme saturation, rather than oxygen concentration, more clearly reveals the relative contributions of autoxidation pathways.
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U2 - 10.1021/bi980529x
DO - 10.1021/bi980529x
M3 - Article
C2 - 9665725
AN - SCOPUS:0032516492
SN - 0006-2960
VL - 37
SP - 10188
EP - 10194
JO - Biochemistry
JF - Biochemistry
IS - 28
ER -