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

点击翻译按钮获取中文摘要

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