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The tonoplast H + ‐pyrophosphatase of radish seedlings: biochemical characteristics
Author(s) -
Pugliarello Maria Chiara,
RasiCaldogno Franca,
De Michelis Maria Ida,
Olivari Claudio
Publication year - 1991
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.1399-3054.1991.tb00103.x
Subject(s) - raphanus , pyrophosphate , pyrophosphatase , inorganic pyrophosphatase , membrane , chemistry , vacuole , proton transport , atpase , nuclear chemistry , biochemistry , sucrose , microsome , chromatography , enzyme , biology , botany , cytoplasm
The activity of the H + ‐pyrophosphatase (H + ‐PPase) was characterized in microsomes from 24‐h‐old radish ( Raphanus sativus L., ev. Tondo Rosso Quarantino) seedlings, which are virtually devoid of the tonoplast H + ‐ATPase. The H + ‐PPase was localized to membranes which roughly comigrated with the plasma membrane in a sucrose density gradient, but clearly separated from plasma membrane when microsomes were partitioned in an aqueous dextran‐polyethylene glycol two‐phase system. The H + ‐PPase activity was strictly dependent on Mg 2+ and on the presence of a monovalent cation (K + =Rb + =NH 3 + Cs + ≫Na + Li + ) and was insensitive to anions such as Cl−, Br−, NO 3 − and SO 4 2‐ . It was inhibited by F−, imidodiphosphate and Ca 2+ . It had a pH optimum between pH 7.5 and 8.5 and was saturated by low concentrations of pyrophosphate (half saturation at 30 μ M pyrophosphate). All of these characteristics are identical to those reported for the tonoplast H + ‐PPase from various plant materials. The functional molecular weight of the H + ‐PPase, measured with the radiation‐inactivation technique was 96 kDa.