title: Isolation and characterization of an abundant and novel 22-kDa protein (SM22) from chicken gizzard smooth muscle.
abstract: Chicken gizzard smooth muscle contains a highly abundant protein (SM22) with an apparent Mr on sodium dodecyl sulfate-polyacrylamide electrophoretic gels of 23,000. The ratio of actin:SM22:tropomyosin in this tissue is estimated to be 6.5(+/- 0.8):2.0(+/- 0.2):1.0. At least three isoelectric isoforms are present in ratios of alpha:beta:gamma of 14:5:1 with alpha the most basic and gamma the most acidic. A method for the purification of SM22 and partial separation of its isoforms is described. Amino acid analyses of purified alpha and beta demonstrate the presence of 1 and 2 half-cystines, respectively, and a lower content of basic amino acids in beta. A value of 22,000 for the Mr of alpha estimated by sedimentation equilibrium indicated its presence as a monomer at physiological ionic strengths. Estimates of the translational frictional coefficient (f/fmin) of alpha calculated from its Stokes radius (25.5 A) and Mr were consistent with its existence as a moderately asymmetric globular protein. Calculations based on its far-ultraviolet CD spectrum provided values of 37% alpha-helix, 31% beta-sheet, 5% beta-turn, and 27% random coil. SM22 was shown not to share functional properties with several proteins of similar Mr and isoelectric point such as myokinase, brain 23-kDa protein, and troponin I. We conclude that it is a novel protein not previously isolated or characterized from any tissue.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002845:Chromatography; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D005590:Fractional Precipitation; D000070559:Gizzard, Non-avian / Q000032:analysis; D007526:Isoelectric Point; D008840:Microfilament Proteins; D008970:Molecular Weight; D009124:Muscle Proteins / Q000302:isolation & purification*; D009130:Muscle, Smooth / Q000032:analysis*; D010446:Peptide Fragments; D011487:Protein Conformation
chemical_list: D000596:Amino Acids; D008840:Microfilament Proteins; D009124:Muscle Proteins; D010446:Peptide Fragments; C058992:Tagln protein, mouse; C051615:transgelin