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The role of Mg 2+ in proton transport by the tonoplast pyrophosphatase in Riccia fluitans vacuoles
Author(s) -
Johannes Eva,
Felle Hubert H.
Publication year - 1989
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1989.tb05649.x
Subject(s) - vacuole , pyrophosphatase , inorganic pyrophosphatase , pyrophosphate , proton transport , chemistry , acridine orange , biochemistry , membrane transport , stereochemistry , enzyme , membrane , cytoplasm , apoptosis
The Mg 2+ ‐dependent activity of the tonoplast pyrophosphatase (PPase) was investigated by measuring proton transport and by using the acridine orange technique on intact vacuoles of the aquatic liverwort Riccia fluitans L. In solutions with both Mg 2+ and pyrophosphate present, a number of complexes are formed, which could all influence the enzymatic and hence the transport activity of the PPase. Therefore, the individual concentrations of these complexes were calculated and their contributions to proton transport across the tonoplast were tested. From these experiments we conclude that Mg 2+ has three different roles: (i) Mg 2+ stimulates transport activity of the PPase. (ii) Mg 2 PP i inhibits PPase‐mediated H + transport, (iii) MgPP i * (= MgPP i 2‐ + MgHPP i ‐ ) is the substrate with an apparent K 1/2 = 5–10 μM, with no discrimination between MgPP i 2‐ and MgHPP i ‐ .