Boerner R J, Barry B A
Department of Biochemistry, University of Minnesota, St. Paul 55108.
J Biol Chem. 1994 Jan 7;269(1):134-7.
Isotopic labeling of Synechocystis sp. PCC 6803 and EPR spectroscopy have been used to demonstrate that photosystem II contains two redox active tyrosines, D and Z (Barry, B. A. and Babcock, G. T. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7099-7103; Boerner, R. J. and Barry, B. A. (1993) J. Biol. Chem. 268, 17151-17154). Another organic radical, M+, has recently been observed in site-directed mutants in which a non-redox active amino acid is substituted at either the putative D or putative Z sites (Boerner, R. J., Bixby, K. A., Nguyen, A. P., Noren, G. H., Debus, R. J., and Barry, B. A. (1993) J. Biol. Chem. 268, 1817-1823; Noren, G. H., and Barry, B. A. (1992) Biochemistry 31, 3335-3342). Here, we use isotopic labeling to determine the chemical identity of M+. Upon incorporation of perdeuterated tyrosine into photosystem II, the M+ EPR signal narrows to approximately 12-13 G. Labeling with 3,5-deuterated tyrosine results in an isotropic doublet with splittings of 11 G. Our results show that M+ is a tyrosine radical with unique spectroscopic properties.
集胞藻PCC 6803的同位素标记和电子顺磁共振光谱已被用于证明光系统II含有两个氧化还原活性酪氨酸，即D和Z（巴里，B.A.和巴布科克，G.T.（1987年）《美国国家科学院院刊》84，7099 - 7103；博纳，R.J.和巴里，B.A.（1993年）《生物化学杂志》268，17151 - 17154）。最近在定点突变体中观察到另一种有机自由基M⁺，在假定的D或假定的Z位点上有一个非氧化还原活性氨基酸被取代（博纳，R.J.，比克斯比，K.A.，阮，A.P.，诺伦，G.H.，德布斯，R.J.和巴里，B.A.（1993年）《生物化学杂志》268，1817 - 1823；诺伦，G.H.和巴里，B.A.（1992年）《生物化学》31，3335 - 3342）。在这里，我们使用同位素标记来确定M⁺的化学身份。将全氘代酪氨酸掺入光系统II后，M⁺电子顺磁共振信号变窄至约12 - 13 G。用3,5 - 氘代酪氨酸标记产生一个各向同性双峰，分裂为11 G。我们的结果表明M⁺是一种具有独特光谱性质的酪氨酸自由基。
