Identification of the tyrosyl residue as the secondary electron donor of Photosystem II reaction center.

1.通过碘化实验鉴定负责结合光系统II电子供体的亚基。用EPR光谱法测定了碘存在下EPR信号的还原动力学，并定量了<125>PS Ⅱ核心复合物制备物中~（12）I在光系统Ⅱ反应中心与D_2-蛋白结合的量。在<125>黑暗中被激发到D2-蛋白中的^ I的量与碘化物引起的信号I缓慢的降低相关。这种相关性表明，黑暗中碘氧化的位点和产生EPR信号的组分Ilslow位于PS II反应中心的D2蛋白上.作为次级电子供体的酪氨酰残基的鉴定，Z。D1-蛋白在光系统II核心复合物中由于二次电子供体Z中碘化物的光氧化而被专门碘化，然后在部分纯化后进行肽图谱分析。 ...更多信息 通过CNDr在蛋氨酸的C-端切割。结果表明，约3 kDa的肽片段是专门碘化的，其N-末端序列表明，它从Gly-128开始，在Met-172结束。根据D1的推导序列，推测该片段含有两个酪氨酰残基，并推测位于类囊体膜内腔侧的Tyr-161被碘化，因此起二次电子供体Z的作用。光系统II反应中心多肽D1和D2的纯化。光系统II反应中心多肽D1和D2是疏水性的和同源的，在SDS存在下通过凝胶渗透HPLC从光系统II反应中心制备物中大规模纯化。对纯化的D1和D2的COOH末端进行了测定，并得出结论，分别为Ala-344和Leu-353。因此，它表明，D1失去了9个氨基酸残基的C-末端在成熟过程中从一个前体，但D2不加工。少

1.Identification of the subunit responsible for binding the electron donor of photosystem II by iodination experiment. The reduction kineties of EPR signal llslow in the prosence of iodido were measured with EPR spectroscopy and the amount of ^<125>I incroparated into the D2-protein in the reaction center of photosystem II was quantitated in a PS II core complex preparation. The amount of ^<125>I that was ineorporated into the D2-protein in the dark was correlated to the reduction of signal llslow by iodide. This correlation indicates that the site of iodide oxidation in the dark and the component giving rise to EPR signal llslow are located on the D2-protein in the PS II reaction center.2. Identification of tyrosyl residue functioning as the secondary electron donor, Z. The D1-protein is exclusively iodinated in the Photosystem II core complex as a result of photooxidation of iodide in the secondary electron donor, Z and then, was subjected to a peptide mapping analysis after partial … More clcavage at C-teminal side of methionine by CNDr. It was shown that a peptide fragment of about 3 kDa was exclusively iodinated and its N-terminal sequence indicated that it starts from Gly-128 and ends at Met-172. From the deduced sequence of D1, this fragment is supposed to contain two tyrosyl residues and it is coneluded that Tyr-161, which is located in the lumenal side of the thylakoid membrane, is iodinated and thus functions as the secondary electron donor, Z.3. Purification of photosystem II rcaction center polypeptides D1 and D2. Photosystem II reaction center polypeptides D1 and D2 ,which are hydrophobic and homologous, were purified on a large scale from photosystem II reaction center preparation by means of gel permeation HPLC in the presence of SDS. COOH-termini of the purified D1 and D2 were determined and were concluded to be Ala-344 and Leu-353, respectively. It is, therefore, shown that D1 loses 9 amino acid residues at C-terminus during maturation from a precursor from but that D2 is not processed. Less