Superoxide Produced in the Heme Pocket of the -Chain of Hemoglobin Reacts with the mg src="http://pubs.acs.org/imag
详细信息 查看全文
- 作者：Chavali Balagopalakrishna ; Omoefe O. Abugo ; Jiri Horsky ; Periakaruppan T. Manoharan ; Enika Nagababu ; and Joseph M. Rifkind
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：September 22, 1998
- 年：1998
- 卷：37
- 期：38
- 页码：13194 - 13202
- 全文大小：104K
- 年卷期：v.37,no.38(September 22, 1998)
- ISSN：1520-4995
文摘
The role of the MG SRC="/images/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-93 cysteine residue in the hemoglobin autoxidation process has been delineatedby electron paramagnetic resonance. At low temperatures (8 K) after incubation at 235 K, free radicalsignals were detected. An analysis of the free radical spectrum produced implies that, besides the superoxideradical expected to be formed during autoxidation, an isotropic free radical is produced with a giso of2.0133. This g value is consistent with that expected for a sulfur radical. Blocking the 
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-93 sulfhydrylgroup with N-ethylmaleimide was found to eliminate the formation of the isotropic radical, but not thesuperoxide. This finding confirms the assignment of the isotropic radical as a thiyl radical originatingfrom the oxidation of the cysteine SH group. A kinetic analysis of the time course for the formation ofboth the superoxide and thiyl radicals is consistent with a reversible electron transfer process betweensuperoxide in the heme pocket of the mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-chains and the cysteine residue. This reaction is expected toproduce both a thiyl radical and a peroxide. Direct evidence for peroxide production comes from thedetection of a transient Fe(III) heme peroxide complex. The significance of the electron transfer processproducing a thiyl radical is discussed. It is shown that the formation of the thiyl radical decreases therate of autoxidation for the mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-chain and reduces heme degradation attributed to the reaction of superoxidewith the heme. The insights gained from these low-temperature studies are believed to be relevant toroom-temperature autoxidation.