Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

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• 作者：Chavali Balagopalakrishna ; Periakarupan T. Manoharan ; Omoefe O. Abugo ; and Joseph M. Rifkind
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：May 21, 1996
• 年：1996
• 卷：35
• 期：20
• 页码：6393 - 6398
• 全文大小：183K
• 年卷期：v.35,no.20(May 21, 1996)
• ISSN：1520-4995

文摘

By low temperature electron paramagnetic resonance wehave detected the formation of afree radical signal during incubation of partially oxygenatedhemoglobin at 235 K. The observed signalhas g_{mages/entities/par.gif">} = 2.0565 andg_{mages/entities/bottom.gif">} = 2.0043, consistent with the previouslyreported values for superoxide. Thepresence of additional EPR signals for oxygen-17 bound hemoglobin, with^(O17-O17)A_{mages/entities/bottom.gif">}=63 G and^(O17-O16)A_{mages/entities/bottom.gif">}= 94 G under identical conditions, confirms the presence of a radicalcontaining two nonequivalent oxygensas required for a superoxide in magnetically inequivalent environments.The superoxide radical has notpreviously been directly detected during hemoglobin autoxidationbecause of its rapid dismutation. Ourability to follow the formation of superoxide for more than 15 min isattributed to its production in thehydrophobic heme pocket where dismutation is slow. The enhancedproduction of this free radical atintermediate oxygen pressures is shown to coincide with enhanced ratesof hemoglobin autoxidation forpartially oxygenated intermediates. The formation of superoxide inthe heme pocket under these conditionsis attributed to enhanced heme pocket flexibility. Greaterflexibility facilitates distal histidine interactionswhich destabilize the iron-oxygen bond resulting in the release ofsuperoxide radical into the heme pocket.