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Volume 334, number 1, 101-105 FEBS 13218 0 1993 Federation of European Biochemical Societies 00145793/93/$6.00

Summary: Volume 334, number 1, 101-105 FEBS 13218
0 1993 Federation of European Biochemical Societies 00145793/93/$6.00
November 1993
Chloroplast thylakoid protein phosphatase reactions are
redox-independent and kinetically heterogeneous
Todd Silverstein**, Luling Cheng, John F. Alien*
Plant Cell Biology, University of Lund, Box 7007, S-220 07 Lund, Sweden
Received 2 September 1993; revised version received 21 September 1993
At least eleven thylakoid proteins become phosphorylated under reducing conditions, and redox titration has identified a common midpoint
potential of Em= +38 ? 4 mV, n = 0.95 2 0.06. In the presence of the phosphatase inhibitor NaF (10 mM), the redox dependency of phosphoryl-
ation is found to be essentially unchanged: Em= +50 ? 3 mV, n = 1.022 0.04. Thylakoid membranes were phosphorylated in the light and then
incubated at various redox potentials for 15min in the dark; no redox dependencywas observed in the dephosphorylation of any of the 17bands
then distinguishable by autoradiography and phosphorimaging. The phosphoprotein phosphatase reactions can be divided arbitrarily into four
kinetic classes: the fastest, class I, includes LHC 11; the moderate class I1 includes D1 and D2; the slow class I11 includes CP43 and the 9 kDa
phosphoprotein; finally,a 19.5kDa protein exhibitedno loss of 32Pat all. In separate experimentswemeasured thylakoid protein dephosphorylation
initiated by changing the redox potential from -140 to +200 mV, in the presence or absence of fluoride. In this case the results are consistent with
at least two kinetically distinguishableclasses of phosphoprotein phosphatase reactions. We concludethat thylakoid protein phosphatase reactions
are kinetically heterogeneous and redox-independent. It follows that the redox dependency of thylakoid protein phosphorylation is a property of
thylakoid protein kinase reactions. Our observed E,,, and n values are consistent with a primary site of kinase redox control at the level of PQ1PQ'-
of the Q, (Qn)site of the cytochrome b6//'complex.


Source: Allen, John F. - School of Biological and Chemical Sciences, Queen Mary, University of London


Collections: Renewable Energy; Biology and Medicine