Zabelin Alexej A, Shkuropatova Valentina A, Shuvalov Vladimir A, Shkuropatov Anatoly Ya
Institute of Basic Biological Problem, Russian Academy of Sciences, Moscow, Region 142290, Russian Federation.
Biochim Biophys Acta. 2011 Sep;1807(9):1013-21. doi: 10.1016/j.bbabio.2011.05.018. Epub 2011 May 27.
Mid-infrared spectral changes associated with the photoreduction of the bacteriopheophytin electron acceptor H(A) in reaction centers (RCs) of the filamentous anoxygenic phototrophic bacterium Chloroflexus (Cfl.) aurantiacus are examined by light-induced Fourier transform infrared (FTIR) spectroscopy. The light-induced H(A)(-)/H(A) FTIR (1800-1200cm(-1)) difference spectrum of Cfl. aurantiacus RCs is compared to that of the previously well characterized purple bacterium Rhodobacter (Rba.) sphaeroides RCs. The most notable feature is that the large negative IR band at 1674cm(-1) in Rba. sphaeroides R-26, attributable to the loss of the absorption of the 13(1)-keto carbonyl of H(A) upon the radical anion H(A)(-) formation, exhibits only a very minor upshift to 1675cm(-1) in Cfl. aurantiacus. In contrast, the absorption band of the 13¹-keto C=O of H(A)(-) is strongly upshifted in the spectrum of Cfl. aurantiacus compared to that of Rba. sphaeroides (from 1588 to 1623cm(-1)). The data are discussed in terms of: (i) replacing the glutamic acid at L104 in Rba. sphaeroides R-26 RCs by a weaker hydrogen bond donor, a glutamine, at the equivalent position L143 in Cfl. aurantiacus RCs; (ii) a strengthening of the hydrogen-bonding interaction of the 13¹-keto C=O of H(A) with Glu L104 and Gln L143 upon H(A)(-) formation and (iii) a possible influence of the protein dielectric environment on the 13¹-keto C=O stretching frequency of neutral H(A). A conformational heterogeneity of the 13³-ester C=O group of H(A) is detected for Cfl. aurantiacus RCs similar to what has been previously described for purple bacterial RCs.
通过光诱导傅里叶变换红外（FTIR）光谱，研究了丝状无氧光合细菌嗜热栖热菌（Cfl.）aurantiaceus反应中心（RCs）中与细菌脱镁叶绿素电子受体H(A)光还原相关的中红外光谱变化。将嗜热栖热菌RCs的光诱导H(A)(-)/H(A) FTIR（1800 - 1200cm(-1)）差谱与之前已充分表征的紫色细菌球形红杆菌（Rba.）sphaeroides RCs的差谱进行了比较。最显著的特征是，球形红杆菌R - 26中在1674cm(-1)处的大负红外带，归因于在自由基阴离子H(A)(-)形成时H(A)的13(1)-酮羰基吸收的损失，在嗜热栖热菌中仅轻微上移至1675cm(-1)。相反，与球形红杆菌相比，嗜热栖热菌光谱中H(A)(-)的13¹-酮C=O吸收带强烈上移（从1588cm(-1)到1623cm(-1)）。数据从以下方面进行了讨论：（i）在嗜热栖热菌RCs的等效位置L143处，用较弱的氢键供体谷氨酰胺取代球形红杆菌R - 26 RCs中L104处的谷氨酸；（ii）在H(A)(-)形成时，H(A)的13¹-酮C=O与Glu L104和Gln L143之间的氢键相互作用增强；（iii）蛋白质介电环境对中性H(A)的13¹-酮C=O伸缩频率可能产生的影响。对于嗜热栖热菌RCs，检测到H(A)的13³-酯C=O基团存在构象异质性，这与之前对紫色细菌RCs的描述类似。
