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oxygen production

Rod Savidge savidge at unb.ca
Thu Dec 5 14:59:14 EST 1996

Can somebody please clarify the following for me.

It is my understanding that enzymically catalyzed photolysis of water to
generate oxygen, protons and electrons occurs at PSII (otherwise known as
the Hill reaction), that oxgygen generation can be demonstrated from
isolated chloroplasts in a cell-free system, and that the PSII core acts as
the catalyst in vitro.

It is also my information that photosynthetic tissue is rich in
superoxide dismutase activity (which produces oxygen and hydrogen
peroxide from superoxide anion) and also in catalase activity, which serves
to produce oxygen by dismutation of hydrogen peroxide.

Assuming the correctness of the assumption that catalase is
compartmentalized exclusively to peroxisomes (glyoxisomes) whereas PSII is
localized to chloroplasts, but not knowing exactly where superoxide
dismutase is, what is the experimental evidence which permits us to teach
that PSII - as opposed to catalase  or SOD - is the primary source of
oxygen production during photosynthesis?   Are there any published
estimates of the relative proportions and absolute amounts of oxygen
generated by each of the three catalytic systems during light and dark
   Rod Savidge, PhD, Professor      |         E-mail: savidge at unb.ca
   Faculty of Forestry and         \|/
      Environmental Management  \   |   /     Phone:  (506) 453-4919
   University of New Brunswick  _\/ | \/_
   Fredericton, NB CANADA          \|/        Fax:    (506) 453-3538
   E3B 6C2                          |

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