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Thermal unfolding equilibria in homodimeric chicken gizzard tropomyosin coiled coils
Author(s) -
Wrabl James,
Holtzer Marilyn Emerson,
Holtzer Alfred
Publication year - 1994
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360341210
Subject(s) - gizzard , chemistry , tropomyosin , biophysics , crystallography , biochemistry , myosin , paleontology , biology
CD studies are presented on thermal unfolding of coiled‐coil homodimers of two genetic variant chains of chicken gizzard tropomyosin (CG‐Tm). The experiments include the effects of cross‐linking both isoforms and the dependence on protein concentration of unfolding in both reduced isoforms, variables not examined in extant work. The general shapes of the unfolding curves for singly cross‐linked species depend on whether the crosslink is at C190 (its site on one isoform) or at C36 (its site on the other). These curves are compared with extant ones for various cross‐linked species of rabbit tropomyosin. The comparison supports the view that the unfolding behavior of cross‐linked species results from a complex interaction of strain at the cross‐link, local variations in structural stability, and loop entropy. The observed concentration dependence of the transition temperature for the uncross‐linked (reduced) species of CG‐Tm is very small (2.9°C) for one variant homodimer and unobservably small (< 2°C) for the other in the 100‐fold concentration range (∼ 0.01–1.0 mg/mL) accessible here. These experimental values of Δ T m are much smaller than are predicted from extant values of the van't Hoff transition enthalpies, calling the latter into question. © 1994 John Wiley & Sons, Inc.