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Kinetic Studies of a (Na + + K + + Mg 2+ ) ATPase in Sugar Beet Roots
Author(s) -
LINDBERG SYLVIA
Publication year - 1976
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.1399-3054.1976.tb03924.x
Subject(s) - chemistry , arrhenius equation , activation energy , sugar beet , kinetics , dithiothreitol , reaction rate constant , atpase , chemical kinetics , analytical chemistry (journal) , nuclear chemistry , enzyme , biochemistry , chromatography , physics , quantum mechanics , horticulture , biology
Kinetic studies of a dithiothreitol treated membrane ATPase fraction from sugar beet roots led to the following conclusions: 1) In the presence of MgATP, Na + and K + stimulate the ATPase activity in different ways following simple Michaelis‐Menten kinetics. Thus separate sites for Na + and K + are suggested. 2) In the absence of K + , Na + acts as an uncompetitive modifier raising the apparent K m and V max for MgATP. 3) In the absence of Na + , K + activates non‐competitively with respect to MgATP. Thus K + increases V max but does not affect the apparent affinity constant. 4) K + and Na + double the rate constants. 5) In the presence of Na + or K + , Mg 2+ in excess acts as a weak inhibitor to Na + and/or K + activity. 6) The temperature‐activity dependence in the 5–40°C interval shows biphasic Arrhenius plots with the transition point between 15–18°C. The activation energy is lowered at temperatures > 18°C.