title: The effect of sulfhydryl blocking groups on the thermal unfolding of alpha alpha tropomyosin coiled coils.
abstract: Equilibrium thermal unfolding curves from circular dichroism are given for alpha alpha tropomyosin and for alpha alpha tropomyosin blocked at C190 by a) carboxyamidomethylation; b) carboxymethylation. Although commonly assumed to be benign, these blocks in fact produce some weakening. All three substances are virtually completely alpha-helical at low T. Fraction helix vs T for parent protein is apparently monophasic (single inflection point). The curve for carboxyamidomethylated protein is very close to that of the parent, but is biphasic, with a small "pretransition". The curve for carboxymethylated protein is prominently biphasic, with a much larger pretransition. Some implications for the molecular model of these equilibria are discussed.
authors.affiliation: Department of Chemistry, Washington University, St. Louis, MO 63130.
authors.forename: M E
authors.initials: ME
authors.lastname: Holtzer
authors.forename: A
authors.initials: A
authors.lastname: Holtzer
authors.forename: D L
authors.initials: DL
authors.lastname: Crimmins
mesh_terms: D007460:Iodoacetamide / Q000494:pharmacology*; D007461:Iodoacetates / Q000494:pharmacology*; D019807:Iodoacetic Acid; D007700:Kinetics; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D013816:Thermodynamics; D014335:Tropomyosin / Q000378:metabolism*
chemical_list: D007461:Iodoacetates; D014335:Tropomyosin; D019807:Iodoacetic Acid; D007460:Iodoacetamide