Abstract

Differential scanning calorimetry (DSC) is unique for studying conformational changes in supramolecular structures because it is immune to interference by the turbidity and other optical artifacts of a sample solution. We have employed DSC to study thermal stability of myosin and actin in their filamentous forms (i.e., thick and thin filaments). The thermal stability of the myosin monomer, as well as polymers, showed remarkable sensitivities to pH and to the ionic strength of the solution. At pH 7.5, the endotherm of myosin filaments was broad and resembled that of the monomer in solution. Reducing the pH to 6.3 split the endotherm of the filament into two major transitions. The first one, with a Tm of 47 degrees C, a delta Hcal of 805 kcal/mol, and a cooperative ratio (CR) of 0.1, was relatively insensitive to the pH changes whereas the second one which represented approximately 80% of the helical structure was pH sensitive. The second transition released 2.17 H+ per mole at 0.17 M KCl and was defined by a Tm of 53.9 degrees C, a delta Hcal of 917 kcal/mol, and a CR of 0.35. The major fragment contributing to the splitting of the endotherm was interpreted to be S-2 because the Tm of purified S-2 in a similar medium also shifted from 39.5 degrees C at pH 7.3 to 49.6 degrees C at pH 6.0. KCl had similar effects on the shape of the endotherm of the thick filament. A decrease of KCl from 0.2 to 0.1 M enhanced the effect of pH on the second transition.(ABSTRACT TRUNCATED AT 250 WORDS) Study holds ProTherm entries: 4003, 4004, 4005, 4006, 4007, 4008, 4009, 4010, 4011, 4012, 4013, 10610, 10611, 10612, 10613, 10614, 10615, 10616, 10617, 10618, 10619, 10620, 10621, 10622, 10623, 10624, 10625, 10626, 10627, 10628, 10629, 10630, 10631, 10632, 10633, 10634, 10635, 10636, 10637, 10638, 10639, 10640, 10641, 10642, 10643, 10644, 10645, 10646, 10647, 10648, 10649, 10650, 10651, 10652, 10653, 10654, 10655, 10656, 10657, 10658, 10659, 10660, 10661, 10662, 10663 Extra Details: additive : EDTA(1 mM),the transition is from native to intermediate supramolecular structures ; thick and thin filaments; actin;,myosin ; cooperativity

Submission Details

ID: AjdAxpQE3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:24 p.m.

Version: 1

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