For the past ten years magnetic circular dichroism (MCD) spectroscopy has made a great progress in various fields of molecular science. This may well be attributed to the progress in polarimeters. The MCD technique has thus far been tested by many authors aiming at making it possible to elucidate complicated electronic spectra and magnetic properties of ions and molecules in their ground and excited states. Of much interest in recent MCD works, π-electron systems have been studied because of the usefulness of MCD. The results obtained thus far suggest that MCD spectra of heme proteins are quite sensitive to changes in the heme electronic structure. Many components of the absorption spectrum can be resolved by MCD, since the Faraday parameters A, B and C of MCD have three different origins. In this article, the recent MCD studies on myoglobin derivatives and related heme proteins, including fundamental concept of MCD spectroscopy, are briefly reviewed.
The mechanism of myosin ATPase was briefly reviewed. Functional significance of the myosin**-product intermediate formed via ATP hydrolysis and of the double-headed structure of myosin in muscle contraction mechanism was critically discussed. The myosin-ADP complex as the predominant intermediate during the Mn(II)-ATP hydrolysis below 10°C, activation of the ATPase activity by actin. and tension development by glycerinated fibers in Mn-ATP below 10°C were described. The latter two are still to be explained. Evidences for the non-identity of the two heads of a myosin molecule were described. Some results of attempts to separate them from each other were mentioned.
The mechanism of calcium transport mediated by Ca2+, Mg2+ ATPase in sarcoplasmic reticulum was briefly discussed in this review. Initially, the recent findings on the main components of the calcium transport system, i.e., Ca2+, Mg2+ ATPase, phospholipid and proteolipid, were shortly reviewed. Next, our scheme for coupling between calcium transport and elementary steps in Ca2+, Mg2+ ATPase was described. Finally, the mechanism of energy transduction in active calcium transport was discussed based on thermodynamic analysis of the ATPase reaction. It was suggested that the observed great change in entropy of the ATPase plays an essential role in the energy transduction.
The most common term which is used for interpreting the physicochemical processes is obviously the free energy change. However, for detailed interpretation they should be discussed in terms of both the enthalpy and entropy values rather than the free energy data alone. It is obvious that the enthalpy values can be most accurately determined by direct calorimetry. Recent development in the calorimetric techniques have enabled their application to the various biochemical processes. In this article calorimetric studies of protein-ligand interaction are reviewed. When the calorimetric measurements are performed at different ligand concentrations, a thermal titration curve is obtained. This method is employed for the analysis of binding site involved in various enzyme and protein molecules. Temperature dependence of enthalpy changes gives a heat capacity change. A large negative value is often observed in the protein-ligand interaction. A magnitude of the heat capacity data is attributed to a change in protein structure accompanied by the ligand-binding. When an ionizable group of a protein molecule participates in the binding reaction, the enthalpy change varies with pH. Thus the enthalpy values obtained at different pHs gives an information about the role of ionizable amino acid residue in the binding site.