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Mechanism for Cd 2+ inhibition of (K + + Mg 2+ )ATPase activity and K + ( 86 Rb + ) uptake join roots of sugar beet ( Beta vulgaris )
Author(s) -
Lindberg Sylvia,
Wingstrand Göran
Publication year - 1985
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.1399-3054.1985.tb01900.x
Subject(s) - chemistry , sugar beet , atpase , chenopodiaceae , kinetics , enzyme , pi , biochemistry , non competitive inhibition , substrate (aquarium) , stereochemistry , nuclear chemistry , biology , physics , quantum mechanics , horticulture , ecology
Steady state kinetics were used to examine the influence of Cd 2+ both on K + stimulation of a membrane‐bound ATPase from sugar beet roots ( Beta vulgaris L. cv. Monohill) and on K + ( 86 Rb + ) uptake in intact or excised beet roots. The in vitro effect of Cd 2+ was studied both on a 12000–25000 g root fraction of the (Na + +K + +Mg 2+ )ATPase and on the ATPase when further purified by an aqueous polymer two‐phase system. The observed data can be summarized as follows: 1) Cd 2+ at high concentrations (>100 μ M ) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd 2+ at concentrations <100 μ M inhibits the specific K + activation at both high and low affinity sites for K + . The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K + <5 m M , the inhibition by Cd 2+ with respect to K + is uncompetitive. In the presence of MgATP and K + >10 μ M , the inhibition by Cd 2+ is competitive. 3) At the low concentrations of K + , Cd 2+ also inhibits the 2,4‐dinitrophenol(DNP)‐sensitive (metabolic) K + ( 86 Rb + ) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP‐insensitive (non metabolic) K + ( 86 Rb + ) uptake is little influenced by Cd 2+ . As Cd 2+ inhibits the metabolic uptake of K + ( 86 Rb + ) and the K + activation of the ATPase in the same way at low concentrations of K + , the same binding site is probably involved. Therefore, under field conditions, when the concentration of K + is low, the presence of Cd 2+ could be disadvantageous.