J. Biol. Chem., Vol. 258, Issue 7, 4214-4219, Apr, 1983
Properties of a Mr = 38,000 phosphoprotein phosphatase. Modulation by divalent cations, ATP, and fluoride
E Shacter-Noiman and PB Chock
A Mr = 38,000 phosphoprotein phosphatase (EC 3.1.3.16) was purified to near
homogeneity from bovine cardiac muscle. The enzyme, classified as a type 2
phosphatase, was not inhibited by the heat-stable protein, inhibitor-2.
Activity on peptide substrates was stimulated considerably by Mn2+ ions.
The individual and combined effects of divalent cations, ATP, and fluoride
were studied in detail employing the phosphonanopeptide
Leu-Arg-Arg-Ala-Ser(P)-Val-Ala-Gln-Leu as the substrate. ATP and fluoride
inhibited enzyme activity completely in the absence of divalent cations.
Mg2+ either reduced or completely prevented this inhibition depending upon
whether Mn2+ was present. Quantitative analysis of the results revealed
that ATP and fluoride do not inhibit by chelation of an essential metal
(e.g. Mn2+). Rather, a plausible model for the combined effects of Mg2+,
Mn2+, ATP, and fluoride on phosphatase activity must assume that each of
these factors acts by binding to individual sites on the enzyme and not to
each other.