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Published on September 11, 2003; 10.1104/pp.103.026633

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Received May 8, 2003
Returned for revision June 20, 2003
Accepted June 27, 2003

Proton Transport in Maize Tonoplasts Supported by Fructose-1,6-Bisphosphate Cleavage. Pyrophosphate-Dependent Phosphofructokinase as a Pyrophosphate-Regenerating System

Anelise Costa dos Santos , Wagner Seixas da-Silva , Leopoldo de Meis , and Antonio Galina *

Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-590, RJ, Brazil

* Corresponding author; email: galina{at}bioqmed.ufrj.br.

The energy derived from pyrophosphate (PPi) hydrolysis is used to pump protons across the tonoplast membrane, thus forming a proton gradient. In a plant's cytosol, the concentration of PPi varies between 10 and 800 µM, and the PPi concentration needed for one-half maximal activity of the maize (Zea mays) root tonoplast H+-pyrophosphatase is 30 µM. In this report, we show that the H+-pyrophosphatase of maize root vacuoles is able to hydrolyze PPi (Reaction 2) formed by Reaction 1, which is catalyzed by PPi-dependent phosphofructokinase (PFP):

During the steady state, one-half of the inorganic phosphate released (Reaction 4) is ultimately derived from F1,6BP, whereas PFP continuously regenerates the pyrophosphate (PPi) hydrolyzed. A proton gradient ({Delta}pH) can be built up in tonoplast vesicles using PFP as a PPi-regenerating system. The {Delta} pH formed by the H+-pyrophosphatase can be dissipated by addition of 20 mM F6P, which drives Reaction 1 to the left and decreases the PPi available for the H+-pyrophosphatase. The maximal {Delta} pH attained by the pyrophosphatase coupled to the PFP reaction can be maintained by PFP activities far below those found in higher plants tissues.




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A. MUSTROPH, G. ALBRECHT, M. HAJIREZAEI, B. GRIMM, and S. BIEMELT
Low Levels of Pyrophosphate in Transgenic Potato Plants Expressing E. coli Pyrophosphatase Lead to Decreased Vitality Under Oxygen Deficiency
Ann. Bot., September 1, 2005; 96(4): 717 - 726.
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