title: Comparison of the properties of the protein phosphatases from avian and mammalian smooth muscles: purification and characterization of rabbit uterine smooth muscle phosphatases.
abstract: Three protein phosphatases were purified to near homogeneity from rabbit uterine muscle. These enzymes are termed rabbit uterine smooth muscle phosphatase (RU SMP)-I, -II, and -IV. RU SMP-I is composed of three subunits (Mr 60,000, 55,000, and 38,000) which comigrated with the subunits of turkey gizzard smooth muscle phosphatase (TG SMP)-I. Ethanol treatment of RU SMP-I dissociated the subunits and led to the purification of its catalytic subunit (Mr 38,000), RU SMP-Ic. Structural homology between the turkey gizzard and rabbit uterine SMP-I is indicated by the cross-reactivity of RU SMP-I with the polyclonal antibodies against TG SMP-I and -Ic. Like TG SMP-II, RU SMP-II is inactive in the absence of divalent cations and can be activated by Mg2+ and Mn2+. However, their electrophoretic profiles on sodium dodecyl sulfate-polyacrylamide gel are different. RU SMP-II shows two bands (Mr 42,000 and 44,000) while TG SMP-II is monomeric (Mr 43,000). Western blot analysis revealed that the 42,000 and 44,000-Da proteins cross-react with anti-TG SMP-II antibodies, suggesting that these proteins share common structural properties. The anti-TG SMP-I and Ic antibodies do not cross-react with RU SMP-II and -IV. Likewise, the anti-TG SMP-II antibodies do not cross-react with RU SMP-I and -IV, implying that these enzymes are distinct. RU SMP-IV is composed of a catalytic subunit (Mr 40,000) and a subunit with a molecular weight of 60,000 or 58,000. All three rabbit uterine smooth muscle phosphatases dephosphorylate the isolated myosin light chains but only RU SMP-IV dephosphorylates heavy meromyosin. However, when the catalytic subunit of RU SMP-I is dissociated from the regulatory subunits, it is active toward heavy meromyosin and exhibits higher activity toward myosin light chains and phosphorylase a than its holoenzyme. The substrate specificity of these enzymes and the effects of ATP, NaF, pyrophosphate, okadaic acid, Mg2+, Mn2+, and Ca2+ on their activities are very similar to those of the turkey gizzard smooth muscle phosphatases.
authors: Department of Biochemistry, University of Saskatchewan, Saskatoon, Canada.
authors: M D
authors: MD
authors: Pato
authors: E
authors: E
authors: Kerc
mesh_terms: D000818:Animals; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004988:Ethers, Cyclic / Q000494:pharmacology; D005260:Female; D005895:Gizzard, Avian / Q000201:enzymology; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000201:enzymology*; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification* / Q000378:metabolism; D011817:Rabbits; D013045:Species Specificity; D013379:Substrate Specificity; D014422:Turkeys; D014599:Uterus / Q000201:enzymology*
chemical_list: D004988:Ethers, Cyclic; D007476:Ionophores; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases