Mg2+-Dependent,cation-stimulated inorganic pyrophosphatase associated with vacuoles isolated from storage roots of red beet (Beta vulgaris L.) |
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Authors: | Robert R Walker Roger A Leigh |
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Institution: | (1) Botany School, University of Cambridge, Downing Street, CB2 3EA Cambridge, UK;(2) Present address: Division of Horticultural Research, C.S.I.R.O., 3505 Merbein, Vic., Australia;(3) Present address: Soils and Plant Nutrition Department, Rothamsted Experimental Station, AL5 2JQ Harpenden, Herts., UK |
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Abstract: | Vacuoles isolated from storage roots of red beet (Beta vulgaris L.) posess a Mg2+-dependent, alkaline pyrophosphatase (PPase) activity which is further stimulated by salts of monovalent cations. The requirement for Mg2+ is specific. Mn2+ and Zn2+ permitted only 20% and 12%, respectively, of the PPase activity obtained in the presence of Mg2+ while Ca2+, Co2+ and Cu2+ were ineffective. Stimulation of Mg2+-PPase activity by salts of certain monovalent cations was due to the cation and the order of effectiveness of the cations tested was K+=Rb+=NH
4
+
>Cs+. Salts of Li+ and Na+ inhibited Mg2+-PPase activity by 44% and 24%, respectively. KCl-stimulation of Mg2+-PPase activity was maximal with 60–100 mM KCl. There was a sigmoidal relationship between PPase activity and Mg2+ concentrations which resulted in markedly non-linear Lineweaver-Burk plots. At pH 8.0, the optimal Mg2+]:PPi] ratio for both Mg2+-PPase and (Mg2++KCl)-PPase activities was approximately 1:1, which probably indicates MgP2O7
2- is the true substrate.Abbreviations BSA
bovine serum albumen
- EDTA
ethylenediamine tetra-acetic acid, disodium salt
- MES
2-(N-morpholino)ethanesulphonic acid
- Mg
T
2+
total magnesium
- Pi
inorganic phosphate
- PPase
inorganic pyrophosphatase
- PPi
inorganic pyrophosphate
- TCA
trichloroacetic acid
- Tris
tris(hydroxymethyl)methylamine |
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Keywords: | Beta Pyrophosphatase Vacuole |
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