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

Abstract

The energy derived from pyrophosphate (PP i ) hydrolysis is used to pump protons across the tonoplast membrane, thus forming a proton gradient. In a plant's cytosol, the concentration of PP i varies between 10 and 800 m, and the PP i concentration needed for one-half maximal activity of the maize (Zea mays) root tonoplast H ϩ -pyrophosphatase is 30 m. In this report, we show that the H ϩ -pyrophosphatase of maize root vacuoles is able to hydrolyze PP i (Reaction 2) formed by Reaction 1, which is catalyzed by PP i -dependent phosphofructokinase (PFP):Fructose-1,6-bisphosphate (F1,6BP) ϩ P i 7 PP i ϩFructose-6-phosphate (F6 P) (reaction 1)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 (PP i ) hydrolyzed. A proton gradient (⌬pH) can be built up in tonoplast vesicles using PFP as a PP i -regenerating system. The ⌬ pH formed by the H ϩ -pyrophosphatase can be dissipated by addition of 20 mm F6P, which drives Reaction 1 to the left and decreases the PP i available for the H ϩ -pyrophosphatase. The maximal ⌬ pH attained by the pyrophosphatase coupled to the PFP reaction can be maintained by PFP activities far below those found in higher plants tissues.

Inorganic phosphate uptake in intact vacuoles isolated from suspension-cultured cells of Catharanthus roseus (L.) G. Don under varying Pi status

“…Protein analysis of membrane vesicles was repeated three times corresponding values for cytoplasmic PPi were around 650 and 300 M for high Pi and low Pi conditions, respectively. These values are similar to those previously reported (Ashihara and Ukaji 1986;Mimura et al 1995b;Maeshima 2000;Costa dos Santos et al 2003). …”

Low Levels of Pyrophosphate in Transgenic Potato Plants Expressing E. coli Pyrophosphatase Lead to Decreased Vitality Under Oxygen Deficiency

“…One possible function of this cycle could be the generation of PPi used for sucrose mobilization via SuSy and UGPase. A comparable mechanism was suggested in maize plants (Costa dos Santos et al, 2003). Here the authors provided evidence for the gluconeogenetic direction of PFP to produce PPi used by the tonoplast PPase.…”

Pathway analysis using 13C‐glycerol and other carbon tracers reveals a bipartite metabolism of Legionella pneumophila

“…Yet, fructose-1,6-bisphosphatase activity in L. pneumophila cell extracts is 10-fold higher than phosphofructokinase activity, indicating that this step in the EMP pathway favors the gluconeogenic rather than the glycolytic direction (Keen and Hoffman, 1984). Interestingly, the putative L. pneumophila phosphofructokinase is homologous to eukaryotic and bacterial PfkA enzymes that do not use ATP but pyro-phosphate as cofactor and are reversible (Arimoto et al, 2002;Costa dos Santos et al, 2003). Thus, L. pneumophila PfkA might also catalyze both the forward (glycolytic) and the reverse (gluconeogenic) reaction.…”