Quantum Yield Controversy: A letter

govindjee gov at uiuc.edu
Mon Jun 22 11:23:37 EST 1998


Dear Photosynthesizers:

I would appreciate your comment on a letter I have prepared for you to
read: it deals with a paper by Warburg et al. (1969) that I believe shows
that Warburg finally obtained the same value on the minimum quantum yield
of photosynthesis (at low light intensity) that everyone else obtained. If
I am wrong, I would like to be corrected. In order to challenge my view,
you will need to read Warburg's 1969 paper(see citation at the end of my
letter). I attach here this letter as an enclosure as well as a pasted copy
in case you cannot open the enclosure. If you receive extra  copies, please
forgive me for the same.

 Your Servant,

Govindjee

[Moderators note:  the attachment has been removed as attachements are not
allowed in this newsgroup due to security concerns.]

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A LETTER TO PHOTOSYNTHESIS COMMUNITY:
A NEW LOOK AT THE QUANTUM YIELD CONTROVERSY BETWEEN EMERSON AND WARBURG by
Govindjee, Department of Plant Biology and Biophysics, University of
Illinois at Urbana-Champaign, 265 Morrill Hall, Urbana, IL 61801-3707
E-mail: gov at uiuc.edu; Fax: 217-244-7246
        I wish to mention here two interesting observations on the question
of the minimum quantum requirement of oxygen evolution (minimum number of
quanta needed to release one molecule of oxygen in photosynthesis).  First
of all, it was William Arnold who was the first person to obtain a measured
value of 8, but did not publish it then because it ran contradictory to the
accepted value of 4, obtained by Otto Warburg (see Arnold, 1991;  and,
Malkin and Fork, 1996, for a full account).  Secondly, Warburg himself
finally published a measured minimum quantum requirement of 12 at low
intensity (that can be extrapolated to a value of 8 as light approaches
zero intensity) (see Fig. 2 and Table 2 in Warburg et al., 1969) [I have
been aware of this for a long time and have mentioned to the others since
1982 when I re-read it; I have read it again yesterday, June 21, 1998, and
decided to send it to you today].  These values are in agreement with
Emerson's values (see Emerson, 1958) and my values (obtained in
collaboration with Rajni Govindjee and Eugene Rabinowitch in 1968) under
conditions dictated by Warburg after Emerson's death in 1959 (see Govindjee
et al., 1968).  After reading Warburg et al. (1969), I have concluded that
Warburg's major concern was that the value of 8 somehow contradicted
Einstein's law of photochemical equivalence (one photon leading to one
photochemical event).  If he had accepted as others did by 1969 that
photosynthesis requires two light reactions and four electrons are
transferred from water to carbon-di-oxide in two steps (i.e., there are 8
primary events), he would have had no difficulty in accepting the measured
minimum quantum requirement of 8 as this would have satisfied Einstein's
law of photochemical equivalency.  Instead Warburg et al. (1969) argued
that their own measured values ( of 12, etc) are not true values of quantum
requirement, and used a contrived (as it was obtained also from oxygen
measurements) method to calculate absorption by an unsubstantiated and, in
my opinion, a hypothetical photolyte (chlorophyll bound to carbonic acid)
which was then used to conclude "the quantum requirement of the splitting
of the photolyte is always 1" confirming Einstein's law of photochemical
equivalence.  Warburg et al. (1969) further state "We donot hesitate to
express here our satisfaction that after the short time of 46 years
(Warburg and Negelein, 1923) truth has now won its war also in the main
reaction of bioenergetics".  The authors failed to mention that their new
measurements were in agreement with the measurements of Emerson and others
and were in conflict with the measured values of Warburg and Negelein
(1923).  No one has doubted the validity of the Einstein's law: the two
light reaction scheme is in perfect agreement with the measured quantum
requirement values of 8-12 at the low light intensities not only of Emerson
and coworkers (including Arnold and myself), but, I emphasize, Warburg
himself (Warburg et al., 1969).  Thus, I believe no controversy need to
exist between Warburg's measured values and those of the others."
REFERENCES

Arnold W (1991) Experiments. Photosynth Res 27: 73-82 (see p. 75, right
column, lines   14-21)

Emerson, R. 1958. The quantum yield of photosynthesis. Ann. Rev. Plant
Physiol. 9:1-    24.

Govindjee, R., Rabinowitch, E.& Govindjee. 1968. Maximum quantum yield and
action       spectrum of photosynthesis and fluorescence in Chlorella.
Biochim. Biophys. Acta        162: 539-544.

Malkin S and Fork DC (1996) Bill Arnold and calorimetric measurements of
the quantum    requirement of photosynthesis- once again ahead of time.
Photosynth Res 48: 41- 46

Warburg O, Krippahl G and Lehman A (1969) Chlorophyll   catalysis and
Einstein's law of         photochemical   equivalence in photosynthesis.
Amer J Bot 56: 961-      971
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Govindjee

Professor of Biochemistry and of Plant Biology, Center of Biophysics and
Computational Biology, University of Illinois at Urbana-Champaign, 265
Morrill Hall, 505 South Goodwin Avenue, Urbana,IL 61801-3707,USA

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
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