Uni‐site catalysis in thylakoids
Open Access
- 20 August 1990
- journal article
- Published by Wiley in FEBS Letters
- Vol. 269 (1) , 247-251
- https://doi.org/10.1016/0014-5793(90)81165-k
Abstract
ATP‐hydrolysis was measured with thylakoid membranes during continuous illumination. The concentrations of free and enzyme‐bound ATP, ADP and Pi were measured using either cold ATP, [γ‐32P]ATP or [14C]ATP. The concentration of free ATP was constant, free ADP and enzyme‐bound ATP were below the detection limit. Nevertheless, [γ‐32P]ATP was bound, hydrolyzed and 32Pi was released. The ADP was not released from the enzyme but cold Pi was bound from the medium, cold ATP was resynthesized and released. A quantitative analysis gave the following rate constants: ATP‐binding kATP = 2·105 M−1s−1, ADP‐release: kADP −2s−1, Pi‐release: kPi = 0.1 s−1. These rate constants are considerably smaller than under deenergized conditions. The rate constant for the release of ATP can be estimated to be at least 0.2 s−1 under energized conditions. Obviously, energization of the membrane, i.e. protonation of the enzyme leads mainly to a decrease of the rate of ATP‐binding, to an increase of the rate of ATP release and to a decrease of the rate of ADP‐release.Keywords
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