PMID: 938646Jun 8, 1976

Studies on the rate-limiting reaction of photosynthetic oxygen evolution in spinach chloroplasts

Biochimica Et Biophysica Acta
T Arnason, J Sinclair


The modulated oxygen polarography has been used to study the rate-determining steps of photosynthetic oxygen evolution in spinach chloroplasts. The rate constant, k, of the reaction has a value of 218 +/- 10 (S.E.) s-1 at 23 degrees C and an activation energy of 7 +/- 2 (S.E.) kcal-mol-1. A kinetic isotope experiment indicated that this step is probably not the water-splitting reaction. These findings resemble previous results with the unicellular alga Chlorella (Sinclair, J. and Arnason, T (1974) Biochim. Biophys. Acta 368, 393-400). In other experiments we changed the pH, O2 concentration and osmolarity of the medium, and treated the chloroplasts with 1 mM NH4Cl without detecting any significant change in k. These results suggest that the step is irreversible. However, a significantly lower value of k, 110 +/- 20 (S.E.) s-1 was obtained when all salts except 1 mM MgCl2 were removed from the medium bathing the chloroplasts.


Dec 19, 1974·Biochimica Et Biophysica Acta·J Sinclair, T Arnason
Feb 25, 1969·Biochimica Et Biophysica Acta·G HindS Izawa


Oct 16, 1992·Biochimica Et Biophysica Acta·R J Debus
May 9, 1979·Biochimica Et Biophysica Acta·J SinclairS Garland
Nov 8, 1979·Biochimica Et Biophysica Acta·H MetznerO Bazlen
Aug 22, 2014·BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology·Karl J NiklasUlrich Kutschera

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