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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >Involvement of two groups in reversal of the bathochromic shift of pharaonis phoborhodopsin by chloride at low pH
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Involvement of two groups in reversal of the bathochromic shift of pharaonis phoborhodopsin by chloride at low pH

机译：两组在低pH值下通过氯化物逆转法老王磷视紫红质的红移

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Pharaonis phoborhodopsin (ppR; or pharaonis sensory rhodopsin II, psRII) is a photophobic receptor of the halobacterium Natronobacterium pharaonis. lambda (max) is at 496 nm, but upon acidification in the absence of chloride, lambda (max) shifted to 522 nm. This bathochromic shift is thought to be caused by the protonation of Asp75, which corresponds to Asp85 of bacteriorhodopsin (bR). The D75N mutant, in which Asp75 was replaced by Asn, had its lambda (max) at approximately 520 nm, supporting this mechanism for the bathochromic shift. A titration of the shift yielded a pK(a) of 3.5 for Asp75. In the presence of chloride, the spectral shifts were different: with a decrease in pH, a bathochromic shift was first observed, followed by a hypsochromic shift on further acidification. This was interpreted as: the disappearance of a negative charge by the protonation of Asp75 was compensated by the binding of chloride, but it is worthy to note that the binding requires the protonation of another proton-associable group other than Asp75. This is supported by the observation that in the presence of chloride, upon acidification, the lambda (max),, of D75N even showed a blue shift, showing that the protonation of a proton-associable group (pK(a) = 1.2) leads to the chloride binding that gives rise to a blue shift. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 36]
机译：Pharaonis phoborhodopsin（ppR;或pharaonis感官视紫红质II，psRII）是盐杆菌Natronobacter pharaonis的憎光受体。 λ（max）在496 nm，但是在不存在氯化物的情况下酸化后，λ（max）移至522 nm。这种红移被认为是由Asp75的质子化引起的，Asp75对应于细菌视紫红质（bR）的Asp85。 D75N突变体（其中Asp75被Asn取代）的λ（最大值）在大约520 nm处，支持这种向红移的机制。滴定位移对Asp75的pK（a）为3.5。在存在氯化物的情况下，光谱变化是不同的：随着pH的降低，首先观察到红移，然后是进一步酸化的蓝移。这被解释为：Asp75的质子化导致负电荷的消失被氯化物的结合所补偿，但值得注意的是，该结合需要除Asp75以外的另一个质子缔合基团的质子化。这得到以下观察结果的支持：在存在氯化物的情况下，酸化后，D75N的λ（最大值）甚至显示出蓝移，表明质子缔合基团的质子化（pK（a）= 1.2）导致氯化物结合导致蓝移。 （C）2000 Elsevier Science B.V.保留所有权利。 [参考：36]

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