In the primary process of the light reactions in photosynthesis, an excited chlorophyll releases an election, followed by sequential charge shifts with high efficiency. Prosthetic groups such as chlorophylls and quinones bind at the reaction center polypeptides. The protein regulates the energy levels and dielectric responses of the prosthetic groups. How the functions of the reaction center protein has been evolved to carry out the best performance in the electron transfer will be discussed.
The experimental studies of protein folding dynamics have made remarkable advances lately. This is attributed to the development of new experimental methods that enable to detect submillisecond dynamics of protein folding as well as to the characterization of folding transition states of small single domain proteins. The characterization of folding intermediates, the elucidation of the processes involved before the formation of folding nucleus and the experimental confirmation of the energy landscape theory are several of important problems that are currently discussed.
We have developed a new technique that allows to monitor mechanical and ligand-binding events in a single myosin molecule simultaneously. We describe how ATPase reaction are temporally related to mechanical events at the single molecule level. The results show that the force generation does not always coincide with the release of bound nucleotide, presumably ADP, but the myosin head produces force several hundreds of milliseconds after bound nucleotide is released. This finding does not support the widely accepted hypothesis that force generation is directly coupled to the release of bound ligands. It suggests that myosin has a hysteresis state which stores chemical energy due to ATP hydrolysis.
Fluorescence correlation spectroscopy (FCS) method has been attractive as an analytical tool, particularly in biophysics and biochemistry, with the recent developments of the method. FCS with confocal optics of microscope and real time correlator equipment achieves analysis of fluorescence species in single molecule level from a very sample area (<1 mm) and volume (~fl) in almost real time (sec ~min). An application to the analysis of enzymatic reaction in solution with FCS is demonstrated as a basis of the analysis to tackle the problems in vivo. The concept of FCS and future view are also discussed.
G-protein coupled receptors (GCR) have been cloned from olfactory, vomeronasal and taste organs. Roles of these receptors in these organs are discussed. Olfactory and gustatory responses are induced via cAMP-dependent pathway, IP3-dependent pathway and second messenger-independent pathway. A single olfactory cell responds to various species of odorants, although a single olfactory cell has only one type of GCR. The responses of mammalian vomeronasal receptor cells to pheromones are induced via IP3. A single rat vomeronasal receptor cell responds only to one species of urine which contains pheromones. The receptor mechanisms of sweet, bitter and umami substances are discussed.
Mutant proteins are useful for study of protein stability. However, it is difficult to explain the changes in stability due to mountain, because contributions of amino acid residues to the conformational stability are quite different, depending on their location. In order to quantify directly the contribution of several factors to the conformational stability of a protein, we determined the thermodynamic parameters of denaturation and the crystal structures for more than 60 mutant human lysozymes. Analyzing this database (stability/structure database), the contribution of some factors to conformational stability of a protein, such as hydrophobic effect, hydrogen bond, and water molecule, could be estimated.