History Question :

Govindjee gov at life.uiuc.edu
Thu Dec 16 14:08:37 EST 1999

Dear Art:
Thanks for your question as to the origin of why light reaction II was
called light reaction II and "I" as "I".Here is my recollection. If anyone
has any other idea, I would like to hear it.

First of all, when Robert Emerson (my Professor) discovered the Emerson
Enhancement Effect (in 1956, 1957, article in Proc Natl Acad Sci,USA) , the
two photosystems were referred to as "Short-wave-length" and
"Long-wavelength" systems. In 1960 (article in Science) Govindjee and
Rabinowitch  found that both systems were sensitized by chlorophyll a, but
one was shortwavelength absorbing, and the other long-wavelength absorbing
form. Lou Duysens and his coworkers (1961 paper in Nature) did the crucial
and key experiment : when they excited red algae with red light (absorbed
by Chlorophyll a) , cytochrome f was oxidized (as was known, I believe) and
THEN when they added green light (absorbed by phycoerythrin) , it became
re-reduced. Thus, Duysens et al. (1961) discovered antagonistic effect of
light I (first one they added) on light II (the second one they added). [ I
recommend that you read Duysens's personal perspective in Photosynthesis
Research  (1989). SEE my web page (under "Announcements") for references to
all the Personal Perspectives, published thus far in Photosynthesis
Research  : http://www.life.uiuc.edu/govindjee] The photosystem that was
sensitized by light I was called Photosystem I and the reaction that it
carried out was Light Reaction I.  Also note that the  first reaction
center chlorophyll to be discovered was P700 ( by Bessel Kok, 1956, 1957 )
and it was much later (1967,1968,1969) that P680 (reaction center
Chlorophyll of PSII) was discovered by H.T. Witt and co-workers.By the way
the reaction center II was named P680-P690 by Rabinowitch and Govindjee
(1965, Scientific American) before its discovery. I would like  to write in
the future an article on the "History of the Evolution of Terms in
Photosynthesis" in some form or the other, if I ever will get time for it.
         Further, someone to think that Photosystem II should have been
called Photosystem I because it appears first in the "Z" diagrams, perhaps,
does not realize that both systems start simultaneously , and, thus their
nomenclature is arbitrary. (Please see Govindjee and Lexa program on
"Photosynthesis and Time"; it is on my web page under "Teaching
         May I add a silly think: why do you call your right hand right, and
left hand left? Why do you say that CO2/{CH2O] redox potential is negative
and that of H2O/O2 is positive? Why not the opposite?
Merry Christmas and a Happy New Year,



Professor Emeritus of Biophysics and of Plant Biology [In theDepartments of
Plant Biology and of Biochemistry  and in the Center of Biophysics and
Computational Biology]; And, member, Graduate Faculty (till August, 2,002)

MAILING ADDRESS: Department of Plant Biology,  University of Illinois at
Urbana-Champaign, 265 Morrill Hall, 505 South Goodwin Avenue, Urbana,IL

Web page address (URL): <http://www.life.uiuc.edu/govindjee/>

Office phone: 217-333-1794; office fax: 217-244-7246

Home address: 2401 South Boudreau, Urbana,IL 61801-6655, USA
Home phone; 217-337-0627; home fax: 217-337-6389
"Let noble thoughts come to you from every side"


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