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.
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Abbreviations
- SMP-II:
-
Smooth Muscle Phosphatase-II
- MOPS:
-
3-[N-Morpholine]propane Sulfonic Acid
- PLC:
-
Phosphorylated Myosin Light Chains
References
Pato MD: Properties of the smooth muscle phosphatases from turkey gizzards. Adv Prot Phosphatases 1: 367–382, 1985
Ingebritsen TS, Cohen P: Protein phosphatases: properties and role in cellular regulation. Science 221: 331–338, 1983
Pato MD, Adelstein RS, Crouch D, Safer B, Ingebritsen TS, Cohen P: The protein phosphatases involved in cellular regulation: 4. Classification of two homogeneous myosin light chain phosphatases from smooth muscle as protein phosphatase from reticulocytes active on protein synthesis initiation factor elF-2 as protein phosphatase-2A2. Eur J Biochem 132: 283–287, 1983
Pato MD, Adelstein RS: Characterization of a Mg2+-de-pendent phosphatase from turkey gizzard smooth muscle. J Biol Chem 258: 7055–7058, 1983
Mackenzie CW III, Bulbulian GJ, Bishop JS: Use of fluoride to inactivate phosphorylase a phosphatase from rat liver cytosol. Biochem Biophys Acta 614: 413–424, 1980
Hiraga A, Kikuchi K, Tamura S, Tsuiki S: Purification and characterization of Mg2+-dependent glycogen synthase phosphatase (phosphoprotein phosphatase IA) from rat liver. Eur J Biochem 119: 503–510, 1981
Li HC: Purification and properties of cardiac muscle phosphoprotein phosphatase and alkaline phosphatase isozymes. In: OM Rosen and EG Krebs (eds) Cold Spring Harbor Conference on Cell Proliferation, Vol. 8, Book A, Protein Phosphorylation. Cold Spring Harbor Laboratory, New York, 1981, pp 441–457
Binstock JF, Li HC: A novel glycogen synthase phosphatase from canine heart. Biochem Biophys Res Commun 87: 1226–1234, 1979
McGowan CH, Cohen P: Identification of two isoenzymes of protein phosphatase 2C in both rabbit skeletal muscle and liver. Eur J Biochem 166: 713–722, 1987
McGowan CH, Campbell DG, Cohen P: Primary structure analysis proves that protein phosphatases 2C1 and 2C2 are isozymes. Biochem Biophys Acta 930: 279–282, 1987
Gupta RK, Moore RD: 31P NMR studies of intracellular free Mg2+ in intact frog skeletal muscle. J Biol Chem 255: 3987–3993, 1980
Kushmerick MJ, Dillon PF, Meyer RA, Brown TR, Krisanda JM, Sweeney HL: 31P NMR spectroscopy, chemical analysis, and free Mg2+ of rabbit bladder and uterine smooth muscle. J Biol Chem 261: 14420–14429, 1986
Pato MD, Adelstein RS: Purification and characterization of a multisubunit phosphatase from turkey gizzard smooth muscle. J Biol Chem 258: 7047–7054, 1983
Adelstein RS, Conti MA, Hathaway DR, Klee CB: Phosphorylation of smooth muscle myosin light chain kinase by the catalytic subunit of adenosine 3′-5′-monophosphatedependent protein kinase. J Biol Chem 253: 8347–8350, 1978
Sellers JR, Pato MD, Adelstein RS: Reversible phosphorylation of smooth muscle myosin, heavy meromyosin, and platelet myosin. J Biol Chem 256: 13137–13142, 1981
Hsiao KJ, Sandberg AR, Li HC: The role of ATP and divalent cations in the regulation of a cardiac phosphorylase phosphatase (phosphoprotein phosphatase) of Mr = 35,000. J Biol Chem 253: 6901–6907, 1978
Li HC: Phosphoprotein phosphatases. In: BL Horecker and ER Stadtman (eds.) Current Topics in Cellular Regulation. Vol. 21. Academic Press, New York, 1982, pp 129–174
Ash DE, Schramm VC: Determination of free and bound manganese (II) in hepatocytes from fed and fasted rats. J Biol Chem 257: 9261–9264, 1982
Schramm VL: Metabolic regulation: could Mn2+ be involved?. In: RS Ochs, RW Hanson and J Hall (eds.) Metabolic Regulation. Elsevier Science Publishers, Amsterdam, 1985, pp 235–239.
Piascik MT, Addison B, Babich M: Ca2+-dependent inhibition of smooth muscle adenylate cyclase activity. Arch Biochem Biophys 241: 28–35, 1985
Steer ML, Levitzki A: The control of adenylate cyclase by calcium in turkey erythrocyte ghosts. J Biol Chem 250: 2080–2084, 1975
Lasker RD, Downs RW, Aurbach GD: Calcium inhibition of adenylate cyclase: studies in turkey erythrocyte and S49 CYC-cell membranes. Arch Biochem Biophys 216: 345–355, 1982
Van de Werve G: Inhibition of liver glycogen synthase phosphatase by calcium: new evidence for an interaction between synthase activation and phosphorylase a. Biochem Biophys Res Commun 102: 1323–1329, 1981
Mvumbi L, Bollen M, Stalmans W: Calcium ions and glycogen act synergisticaly as inhibitors of hepatic glycogen - synthase phosphatase. Biochem J 232: 697–704, 1985
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Pato, M.D., Kerc, E. Regulation of smooth muscle phosphatase-II by divalent cations. Mol Cell Biochem 101, 31–41 (1991). https://doi.org/10.1007/BF00238435
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DOI: https://doi.org/10.1007/BF00238435