Kaoru Kometani

Study of the Dipolar Relaxation by a Continued Fraction Representation of the Time-Correlation Function

The dipolar relaxation is discussed by a continued fraction representation of time-correlation function. A particular attention is given to stochastic processes in the liquid state where the molecular Brownian motion is in the vicinity of the Markovian process. It is shown that the correlation or relaxation time of such interesting dynamical variables as angular momentum, torque, and kinetic energy can be estimated from the moments of infrared absorption spectra. Useful discussions are given to make the relation between the dipolar relaxation and the time dependence of these dynamical variables clear.

Enthalpy, entropy and heat capacity changes induced by binding of calcium ions to cardiac troponin C☆

Microcalorimetric titrations have been used to study the binding of Ca2+ to cardiac troponin C. Measurements were made both in the presence and in the absence of Mg2+, and at temperatures of 5 degrees, 15 degrees and 25 degrees C. Changes in enthalpy, entropy and heat capacity of troponin C associated with Ca binding have been determined. Cardiac troponin C exhibited a decrease in enthalpy and an increase in entropy associated with Ca binding. Enthalpy changes increased linearly with temperature, indicating that the Ca binding causes negative changes in the heat capacity of troponin C. These results show that the Ca binding causes a strong hydrophobic effect and a tightening of the molecular structure of cardiac troponin C.

Dependence of the Shortening Heat on Sarcomere Length in Fibre Bundles from Frog Semitendinosus Muscles

The relation between shortening heat and sarcomere length was studied using fibre bundles dissected from frog semitendinosus muscles, as well as using whole muscles. The velocity of shortening was at its maximum. The unstimulated muscles showed a large thermoelastic absorption of heat when released at long muscle lengths. However the sarcomere length at which this thermoelasticity started to appear was longer, by at least 0.3 micron per sarcomere, in fibre bundles than in whole muscles. At the same time the amount of heat absorbed was decreased in fibre bundles. The shortening heat in fibre bundles at the sarcomere lengths ranging from 2.17 to 2.74 microns, for which no correction for the thermoelasticity was necessary, decreased linearly with sarcomere length. The shortening heat in fibre bundles at longer lengths and in whole muscles was corrected by subtracting the thermoelastic heat absorption measured separately by releasing unstimulated muscles. After the correction the shortening heat showed an almost similar dependence on sarcomere length in the range from 2.0 to 3.7 microns to that seen in fibre bundles in the sarcomere length range of 2.17 to 2.74 micron.

HEAT CAPACITY CHANGES IN CALCIUM AND MAGNESIUM BINDING TO TROPONIN

This chapter elaborates a study analyzing heat capacity changes in calcium and magnesium binding to troponin. A microcalorimetric titration with Ca 2+ or Mg 2+ was performed at pH 7 and at different temperatures of 5, 15 and 25°C on rabbit skeletal muscle troponin from which almost all Ca and Mg had been removed by passing a column of chelating resin. The enthalpy changes associated with the binding of both the first and the second 1 mole Ca 2+ per mole metal-free troponin in the absence of Mg show large negative temperature dependence. Thus the heat capacity change (Δ C p °), obtained from the temperature dependence of ΔC° has a large negative value of about −1 kJ mol −1 K −1, which is characteristic of the hydrophobic effect. The binding of the first 1 mole of Mg also shows the similar negative Δ C p °. For the further binding of Ca 2+ Δ C p ° becomes smaller but is substantially negative. The negative Δ C p ° associated with the binding of Ca 2+ to the two high-affinity sites remains substantial in the presence of 1 mM Mg 2+ .