Regulation of smooth muscle phosphatase-II by divalent cations |
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Authors: | Mary D Pato Ewa Kerc |
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Institution: | (1) Department of Biochemistry, University of Saskatchewan, S7N 0W0 Saskatoon, Saskatchewan, Canada |
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Abstract: | Summary Smooth Muscle Phosphatases II (SMP-I1) which has been purified from turkey gizzards and previously classified as protein phosphatase 2C, is inactive in the absence of divalent cations. Study of the activation of SMP-II by Mg2+ and Mn2+ revealed differences in the modes of activation by these cations. The maximal activation elicited by Mg2+ is 1.5–2.5-fold higher than the maximal Mn2+ activation. However, the latter is achieved at a lower concentration than the maximal Mg2+-activation. Furthermore, at low cation concentrations ( 2 mM), the Mn2+-activated activity is higher than the Mg2+-activated activity. In the presence of both cations, the effect of Mn2+ predominates suggesting that the affinity of the enzyme for Mn2+ is greater than for Mg2+. In contrast to Mg2+ and Mn2+, Ca2+ does not activate SMP-II but it was observed to antagonize the effects of Mg2+ and Mn2+. Ca2+ acts as a competitive inhibitor of Mg2+. However, the inhibitory effect at high Ca2+ concentrations is not completely reversed by increasing the Mg2+ concentration. Mn2+ activation is also inhibited by Ca2+ but to a lesser extent. Ca2+ cannot completely inhibit Mn2+-activation suggesting that SMP-I1 has greater affinity for Mn2+ than for Ca2+. The finding that Ca2+ inhibits the activation of SMP-II raises the possibility that Ca2+ may be a regulator of SMP-II in vivo.Abbreviations SMP-II
Smooth Muscle Phosphatase-II
- MOPS
3-N-Morpholine]propane Sulfonic Acid
- PLC
Phosphorylated Myosin Light Chains |
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Keywords: | type 2C protein phosphatase smooth muscle |
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