The effect of beryllium on K+-activated phosphatase was investigated. Preincubation of the enzyme preparation with BeCl2 in the presence of Mg2+ caused reduction of K+-activated phosphatase activity, while preincubation with BeCl2 only caused no reduction. Addition of K+, Rb+ or NH4+ but not Li+ with Mg2+ and BeCl2 during preincubation increased the inhibition rate. Under the same conditions, Na+ decreased the rate of inhibition. This protective effect of Na+ was greatest in the absence of K+ and decreased with increase in the concentration of K+. The effects of cations on the inhibition of K+-activated phosphatase by beryllium were compared with their effects on that of (Na+ + K+)-activated ATPase [ATP phosphohydrolase, EC 3. 6.1. 3] and results suggested that there is a close linkage between these two enzyme activities. It also seemed that K+ interacted with the enzyme even in the absence ofp-nitrophenyl phosphate and that this interaction was intimately related with the activation of Reactivated phosphatase by K+. Results of kinetic analyses of the activation of Reactivated phosphatase by K+ and the effect of ouabain on the inhibition rate indicated that there are at least two different ways of interaction of K+ with enzyme.
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Toda et al. (1971) studied this question.