Electrostatic properties of protein molecules have essential roles in their specific functions and their structural stabilization. However, there are not any effective methods to detect the local field directly. Moreover, since the protein-solvent system is quite heterogeneous from a dielectric point of view, it has been difficult to analyze quantitatively by any theoretical approaches. In the present article, these problems are reviewed and the recent developments are introduced.
The signal transduction mechanism of opioid receptors was studied in reconstitution experiments with GTP-binding protein. μ-Opioid receptor exclusively purified from rat brains was reconstituted with purified Gi or Go in phosphatidylcholine vesicles. The μ-agonist-displacement activity of antagonist binding was markedly increased by reconstitution with Gi or Go. The μ-agonist stimulated G-protein activities in both reconstituted vesicles. From the experiment that the recovery of agonist-stimulation of G-protein activity was additive when Gi and Go were simultaneouly reconstituted in brain membrane preparations, it is suggested that μ-receptors exist in μi and μo, separately coupled to Gi and Go, respectively.
Up to now three different DNA binding modes have been proposed. One is the α-helix represented by the helix-turn-helix structure of prokaryotic repressors and eukaryotic homoeotic gene products. Another is the antiparallel β-sheet found in G5BP and DBP II. The other is the Zn-finger originally suggested for TF IIIA. The fourth quite new mode of DNA binding was proposed for histones H1 and H2B and then generally found in many gene reguratoly proteins. This is a repeat of β-turns composed of Ser(Thr)-Pro-X-X sequences.
Changes in membrane elastic modulus were measured for intestinal brush border on activation of its Na+-glucose co-transport, and for such secretory granules as chromaffin and zymogen on rise of free [Ca2+]. It is suggested that an increase in membrane flexibility is strongly correlated with activation of such biological functions as transport and exocytosis.
The periaxonal K+-accumulation is markedly large in the squid giant nerve fiber. In this preparation, I have established a method to control the periaxonal K+ concentration. The method is promising for precise kinetic analyses of ionic channels in the squid axon, and thus will make the axon a useful model for the study of K+ dynamics in the brain.
Antibody against the 23 kilodalton fragment of myosin head abolished active tension generation of the fibers, but did not block their assumption of a rigor state nor their release from this state by ATP. The antigenic sites are located at 140-180Å from the head-rod junction of myosin by electron microscopy.
Protein inhibitors of proteinases are as ubiquitous as proteinases. The interaction of serine proteinases with their cognate inhibitors is now one of the best understood of proteinprotein associations, though physiological functions of these inhibitors are not clear. This review briefly describes the classification and inhibitory mechanism of serine proteinase inhibitors. Possible physiological roles of inhibitors of plant origin are also introduced.