Resonance Raman Characterization of the Heme Domain of Soluble Guanylate Cyclase
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- 作者：Johannes P. M. Schelvis ; Yunde Zhao ; Michael A. Marletta ; and Gerald T. Babcock
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：November 17, 1998
- 年：1998
- 卷：37
- 期：46
- 页码：16289 - 16297
- 全文大小：103K
- 年卷期：v.37,no.46(November 17, 1998)
- ISSN：1520-4995
文摘
We report the resonance Raman characterization of the heme domain of rat lung solubleguanylate cyclase (sGC) expressed in Escherichia coli. Like heterodimeric sGC isolated from bovinelung, the sGC heme domain [
1(1-385)] and its heme ligand mutant H105G(Im) contain a stoichiometricamount of heme, which is five-coordinate, high-spin ferrous in both 1(1-385) and chemically reducedH105G(Im). In the presence of NO, both 1(1-385) and H105G(Im) form a five-coordinate nitrosylheme complex with a 
(Fe-NO) value of 525 cm-1 and a (NO) value of 1676 cm-1. For the first time,the Fe-N-O bending mode near 400 cm-1 has been identified in a five-coordinate nitrosyl heme complex.Both 1(1-385) and H105G(Im) form a six-coordinate, low-spin complex with CO. We find evidencefor two binding conformations of the Fe-CO unit. The conformation that is more prevalent in 1(1-385) has a (Fe-CO) value of 478 cm-1 and a 
(Fe-C-O) value of 567 cm-1, whereas the dominantconformation in H105G(Im) is characterized by a (Fe-CO) value of 495 cm-1 and a (Fe-C-O) valueof 572 cm-1. We propose that in the dominant conformation of H105G(Im)-CO the Fe-CO unit ishydrogen bonded to a distal residue, while this is not the case in 1(1-385). Reexamination of sGCisolated from bovine lung tissue indicates that it also has two binding conformations for CO; the morepopulated form is not hydrogen-bonded. We propose that the absence of hydrogen-bond formation betweena distal residue and exogenous ligands is physiologically relevant in lowering the oxygen affinity ofheterodimeric sGC and, therefore, stabilizing the ferrous, active form of the enzyme under aerobicconditions.
1(1-385)] and its heme ligand mutant H105G(Im) contain a stoichiometricamount of heme, which is five-coordinate, high-spin ferrous in both 1(1-385) and chemically reducedH105G(Im). In the presence of NO, both 1(1-385) and H105G(Im) form a five-coordinate nitrosylheme complex with a (Fe-NO) value of 525 cm-1 and a (NO) value of 1676 cm-1. For the first time,the Fe-N-O bending mode near 400 cm-1 has been identified in a five-coordinate nitrosyl heme complex.Both 1(1-385) and H105G(Im) form a six-coordinate, low-spin complex with CO. We find evidencefor two binding conformations of the Fe-CO unit. The conformation that is more prevalent in 1(1-385) has a (Fe-CO) value of 478 cm-1 and a (Fe-C-O) value of 567 cm-1, whereas the dominantconformation in H105G(Im) is characterized by a (Fe-CO) value of 495 cm-1 and a (Fe-C-O) valueof 572 cm-1. We propose that in the dominant conformation of H105G(Im)-CO the Fe-CO unit ishydrogen bonded to a distal residue, while this is not the case in 1(1-385). Reexamination of sGCisolated from bovine lung tissue indicates that it also has two binding conformations for CO; the morepopulated form is not hydrogen-bonded. We propose that the absence of hydrogen-bond formation betweena distal residue and exogenous ligands is physiologically relevant in lowering the oxygen affinity ofheterodimeric sGC and, therefore, stabilizing the ferrous, active form of the enzyme under aerobicconditions.