[Molar extinction of pigment in the reaction center of photosystem II chloroplasts].

The absolute spin number in the Photosystem I chloroplast fragments from Vicia faba plant photooxidized in the presence of silicomolybdate has been carefully measured by means of camparison of ESR signals of P680-centers and of nitroxyl free radical aqueous solution. The data obtained together with simultaneous measurement of light-induced bleaching centered at 680 nm have been used to determine the molar extinction of reduced P680-center epsilon680 = 0.66 . 10(5) M-1 cm-1.