Reexamination of the Hyper Thermodynamic Stability of Asymmetric Cyanomet Valency Hybrid Hemoglobin, (+CN-
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- 作者：Naoya Shibayama ; Hideki Morimoto ; and Satoshi Saigo
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：April 15, 1997
- 年：1997
- 卷：36
- 期：15
- 页码：4375 - 4381
- 全文大小：140K
- 年卷期：v.36,no.15(April 15, 1997)
- ISSN：1520-4995
文摘
It has been reported that hybridization of the equimolar mixtureof cyanomethemoglobin anddeoxyhemoglobin through dimer exchange reaction results inestablishment of an approximately binomial(1:2:1) equilibrium distribution of these parental hemoglobins andtheir hybrid molecule,(
+CN-
beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">), within several days under anaerobic conditions at pH 7.4, 21.5
C, leading to a hyper (i.e., about170 times) thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">)relative to the stability of the other diligandedspecies at pH 7.4, 21.5 C [Daugherty, M. A., Shea, M. A., Johnson,J. A., LiCata, V. J., Turner, G. J.,& Ackers, G. K. (1991) Proc. Natl. Acad. Sci.U.S.A. 88, 1110-1114]. To examinewhether the published"binomiality" for this deoxy-cyanomet hybrid system reallyreflects the thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">), we used abinomial (1:2:1) equilibrium distribution of the equimolar mixture ofcyanomethemoglobin and fully oxygenated hemoglobin as a starting condition, andthen this system was rapidlydeoxygenated. We found that the relative population of the hybridwas reduced to 8.6% of the total upondeoxygenation. It was also found that the hybridization experimentunder anaerobic conditions was notallowed to continue for a long time due to a valency exchange reactionbetween deoxy and cyanometderivatives. For instance, a 48 h incubation resulted in theoxidation of 44% of Fe2+ to Fe3+ hemesinthe original deoxyhemoglobin and the reduction of 42% ofFe3+ to Fe2+ hemes in theoriginalcyanomethemoglobin. These results suggest that a real distributionof the deoxy-cyanomet hybrid systemat equilibrium is fairly far from 1:2:1 (binomial distribution), andthe thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">)is less than one-tenth of the hyperstability previously reported.In addition, most ofthe previous results on deoxy-cyanomet valency hybrids placed underlong anaerobic conditions shouldbe subject to reexamination due to possible valency exchangereactions.
+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">), within several days under anaerobic conditions at pH 7.4, 21.5C, leading to a hyper (i.e., about170 times) thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">)relative to the stability of the other diligandedspecies at pH 7.4, 21.5 C [Daugherty, M. A., Shea, M. A., Johnson,J. A., LiCata, V. J., Turner, G. J.,& Ackers, G. K. (1991) Proc. Natl. Acad. Sci.U.S.A. 88, 1110-1114]. To examinewhether the published"binomiality" for this deoxy-cyanomet hybrid system reallyreflects the thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">), we used abinomial (1:2:1) equilibrium distribution of the equimolar mixture ofcyanomethemoglobin and fully oxygenated hemoglobin as a starting condition, andthen this system was rapidlydeoxygenated. We found that the relative population of the hybridwas reduced to 8.6% of the total upondeoxygenation. It was also found that the hybridization experimentunder anaerobic conditions was notallowed to continue for a long time due to a valency exchange reactionbetween deoxy and cyanometderivatives. For instance, a 48 h incubation resulted in theoxidation of 44% of Fe2+ to Fe3+ hemesinthe original deoxyhemoglobin and the reduction of 42% ofFe3+ to Fe2+ hemes in theoriginalcyanomethemoglobin. These results suggest that a real distributionof the deoxy-cyanomet hybrid systemat equilibrium is fairly far from 1:2:1 (binomial distribution), andthe thermodynamic stability of(+CN-beta2.gif" BORDER=0 ALIGN="middle">+CN-)(beta2.gif" BORDER=0 ALIGN="middle">)is less than one-tenth of the hyperstability previously reported.In addition, most ofthe previous results on deoxy-cyanomet valency hybrids placed underlong anaerobic conditions shouldbe subject to reexamination due to possible valency exchangereactions.