Recent studies on thermal properties of globular proteins are reviewed with emphasis on conformational transitions. In many cases, thermal denaturation of globular proteins can be interpreted well by the two-state approximation whose validity has been tested calorimetrically. Significant deviations from the two-state approximation were observed in some cases, which shows the existence of stable intermediate states. Existence of a prodenaturational stage has been suggested by gradual increase of heat capacity prior to the denaturational stage. Thermal denaturation of the protein was also observed in a crystalline state. The melting temperature of crystalline lysozyme changes reversively from aobut 70 to 200°C depending upon the water content of the crystal. Merit of studies in a crystalline state is discussed.
Bacterial motility and chmotaxis peported recently were reviewed. The bacterial flagellum consists of the three morphological components; a basal membrane, a proximal hook and a helical filament. Amino acid sequence of flagellin, the subunit protein of the helical filament, was determined. Amino acid composition of the hook protein is now in progress. Biochemical nature of the basal membrane, a flagellar motor, is not clear. A hydrodinamic model of the propulsion of the flagellated bacteria was studied. Furthermore, it has been found that the propulsive force of flagellated bacteria is generated not by the propagation of helical waves but by the filament rotation. Energy source of motility and chemotaxis were found to be intermediates of oxidative phosphorylation and ATP, respectively. The probrems of the flagellar motility were discussed genetically, biochemically and optical microscopically.
The development of stopped-flow technique in recent years has enabled the biochemists to study the kinetics and mechanisms of the fast conformation change of biopolymers in solution. This article outlines the experimental technique of the stopped-flow method and areas in which it has been used. Two applications to problems that are of biological interest are discussed in detail; the one is the application to the studies on the unwinding-rewinding reaction of poly nucleic acid, and the other is the unfolding-refolding reactions of proteins.
Resonance Raman Spectra of heme proteins including hemoglobin (Hb), myoglobin (Mb), cytochrome-c (cyt-c), cyt-c3, cyt-b5 and modified (alkylated) cyt-c were measured in their reduced and oxidized states at various pH values. Raman spectra of single crystals of myoglobin derivatives were also measured and it was found that there are some structural changes of hemes on crystallization. The analysis of Raman spectra of Hb and Mb derivatives led us to conclude that the iron-ligand bonding in HbNO and MbNO is rather Fe3+-NO- than Fe2+-NO and also that the same type of bonding is deduced for external ligands including C2H5NC, CO and O2. Good correspondence of Raman lines of cyt-b5 with cyt-c, cyt-c3 and cyt-f revealed that all the Raman lines are mainly due to the porphyrin skeleton although the vibrational coupling between peripheral substituents and the ring skeleton causes the frequency shift and intensity change of Raman lines. The present results suggest that two ligands of iron in cyt-f may possibly be His (18) and Met (62).