Fourier Transform Infrared Evidence against Asp 99 Protonation in Hemoglobin: Nature of the Tyr 
详细信息 查看全文
- 作者：Xuehua Hu ; Lisa A. Dick ; and Thomas G. Spiro
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：June 30, 1998
- 年：1998
- 卷：37
- 期：26
- 页码：9445 - 9448
- 全文大小：61K
- 年卷期：v.37,no.26(June 30, 1998)
- ISSN：1520-4995
文摘
The Tyr 
mages/gifchars/alpha.gif" BORDER=0>42-Asp mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">99 intersubunit H-bond stabilizes the Tquaternary structure in hemoglobin(Hb) tetramers. We had proposed that Tyr mages/gifchars/alpha.gif" BORDER=0>42 acts as an acceptorin this H-bond, because the tyrosineY8a/8b and Y7a' UVRR (ultraviolet resonance Raman) bands shift indirections opposite to those expectedif tyrosine is an H-bond donor. If Asp mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">99 is the H-bond donor,then it must be protonated in the T state,and would be a previously unrecognized contributor to the Bohr effect.This implication was strengthenedby the discovery that an R-minus-T difference FTIR (Fourier transforminfrared) band at 1693 cm-1,which might be a signal from protonated carboxylate, is missing in HbKempsey, a mutant in which Aspmages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">99 is replaced by Asn. However, we now find that this FTIRsignal is insensitive to 13C-labeling of theaspartate residues in Hb, and cannot arise from protonated Asp mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">99.There are no other difference signalsin the 1700 cm-1 region at a sensitivity ofone COOH group. We conclude that Asp mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">99 is notprotonated,and that the anomalous UVRR shifts must arise from compensatingpolarization of the Tyr mages/gifchars/alpha.gif" BORDER=0>42 OH.Candidates for this compensation are the H-bond donated by the Aspmages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">94 backbone NH, and the nearbypositive charge of Arg mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">40.