Recent advances in the study of ribozymes are summarized. One class of ribozymes consists of three functionally different domains which are a recognition unit, a catalytic core unit and an activator unit. The ribozymes are also associated with activator protein (s) in vivo. These four functional units are independent modules. New discoveries on the origin and evolution of intron ribozymes are presented. There are two different origins of these ribozymes. The relationship between the ribozyme and spliceosome is not clear. Attempts to redesign ribozymes as antiviral reagents (RNA restriction enzymes) are also illustrated.
A molten globule state has been assumed to be a major intermediate of protein folding. The conformational stability of the acidic molten globule state of several proteins and the corresponding state of a synthetic model polypeptide is determined by the balance of the electrostatic repulsive forces, which favor the extended unfolded state, and the opposing forces mainly hydrophobic interactions, which favor the compact molten globule state.
In recent years, some important findings, which promoted understanding of the visual cycle, have been reported. For example, (1) the enzymatic process of retinoid isomerization was detected in the vertebrate retinal pigment epithelium cells, (2) finding of a novel retinal-binding protein completed the visual cycle in the squid photoreceptor cells, and (3) the temporary formation of 11-cis-3-OH-retinol on the light-dependent synthesis of visual pigment was demonstrated in the eye of Drosophila. Based on these new findings, matabolic processes of visual pigments both in vertebrates and invertebrates are discussed.
Intramembrane charge movement (IMCM) in skeletal muscle cells has been proposed to underlie the process leading to Ca2+ release from the sarco-plasmic reticurum. The dihydropyridine (DHP) receptor in transverse-tublar membrane is suggested to be responsible for the excitation-contraction coupling (E-C coupling). The skeletal muscle cells in dysgenic mice are characterized by a dramatic reduction of DHP receptor and absence of E-C coupling. We have recorded IMCM in skeletal muscle cells from normal and dysgenic mouse fetuses. The amount of maximum charge in mutant muscle was less than 30% of that in normal muscle. Nifedipine, a DHP derivative, reduced the amount of charge in normal muscle by 40%, but did not in the dysgenic muscle. The results suggest that the DHP sensitive component is essetial if IMCM plays a key role in the signal-transduction mechanism underlying E-C coupling.
Positron emission tomography (PET) provides us an opportunity for quantitative measurement of the metabolism in living humans. During the last decade, a lot of fruitful results have been obtained from the PET studies in the brain, heart and cancer research. In this review, neuroreceptor studies with positron labeled receptor ligands using PET was introduced. Visualization of specific binding site in the human brain and quantification of binding potential was described with special reference to 11C-N-methylspiperone, a ligand for dopamine D2 receptor.
Lattice model is useful in studying dynamics of populations with local interaction and spatial structure. Here the quasi-steady state is analysed by decoupling approximation and computer simulation. The condition for population extinction in a lattice model is qualitatively different from a corresponding Lotka-Volterra system.