光合作用机理研究的新突破

欧洲同步辐射装置(ESRF)的研究人员在-260度低温环境中，利用X-rays研究菠菜光合系统II的放氧复合体（oxygen-evolving  complex）动力学，解析了Kok  cycle其中一个未知步骤。研究结果发表在《Science》上。

Using  sunlight  to  power  our  homes  and  offices  is  an  unaccomplished  dream  due  to  the  still  inefficient  technology  for  a  better  use  of  solar  energy.  The  study  of  photosynthesis  in  plants  could  provide  new  clues  by  explaining  how  they  absorb  almost  100%  of  the  sunlight  reaching  them,  and  how  they  transform  it  into  other  forms  of  energy.  Researchers  Michael  Haumann  and  Holger  Dau,  from  the  Freie  Universität  Berlin,  used  the  X-ray  source  of  the  European  Synchrotron  Radiation  Facility  (ESRF)  to  investigate  the  kinetics  of  the  photosynthesis  process.  They  have  confirmed  the  existence  of  a  fifth  step  in  the  catalysis  process  converting  water  into  oxygen,  and  have  published  their  results  in  Science.

Chlorophyll  in  plants  absorbs  light  from  the  sun,  which  then  becomes  energy  used  by  the  so-called  "oxygen-evolving  complex"  to  catalyse  the  splitting  of  water  into  molecular  oxygen.  This  complex  contains  four  manganese  and  one  calcium  atom  that  are  known  to  be  at  the  centre  of  the  catalytic  reaction.  Five  intermediate  states  have  been  proposed  in  the  process  of  photosynthesis  -  a  cycle  known  as  the  "Kok  cycle"  -  but  only  four  had  been  proved  until  recently.  With  the  help  of  the  ESRF,  scientists  have  been  able  to  identify  the  missing  state,  which  is  particularly  important  because  it  is  directly  involved  in  the  molecular  oxygen  formation.  They  suggest,  furthermore,  an  extension  of  the  "Kok  cycle"  with  an  additional  intermediate  and  propose  a  new  reaction  mechanism  on  a  molecular  basis  for  the  release  of  dioxygen.  This  gives  new  insight  into  the  mechanism  of  photosynthesis.

In  order  to  study  this  process,  the  use  of  synchrotron  light  was  crucial:  "A  very  intense  and  stable  X-ray  beam  is  necessary  to  perform  this  study  on  such  a  complex,  highly  diluted  protein  present  in  the  investigated  spinach  sample",  explains  Pieter  Glatzel,  head  of  beamline  ID26,  where  the  experiments  were  carried  out.  The  researchers  measured  the  fluorescence  from  the  sample  that  is  emitted  after  excitation  with  X-rays. (责任编辑：泉水)

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光合作用机理研究的新突破