X-RAY-ABSORPTION LINEAR DICHROISM SPECTROSCOPY (XALDS) ON THE PHOTOSYSTEM-II MANGANESE COMPLEX - RADIATION-DAMAGE AND S-1-STATE K-EDGE SPECTRA

X-ray absorption spectroscopy (XAS) at the Mn K-edge is used to unrave l the structure of the oxygen-evolving manganese complex which is embe dded in the Photosystem II (PS II) protein complex; measurements on mu ltilayers of PS II-containing membrane sheets provide angular informat ion (XALDS). (1) By XAS and electron spin resonance (ESR) we investiga ted origin and characteristics of the radiation damage which is caused by prolonged exposure to intense synchrotron radiation. (2) By a deri vative analysis of XALD-edge spectra, eight distinct transitions are r esolvable (a to h). In contrast to the transitions c to e of the edge rise, f (6562 eV) and g (6565 eV) on top of the Mn K-edge exhibit char acteristics of a formally-allowed electric dipole transition with an a ngle between transition dipole and membrane normal greater (f) and sma ller (g) than the magic angle (= 54.7 degrees), respectively.