Gating kinetics of the Ca channel have been studied recently by applying a cell attached patch clamp and a whole cell recording techniques to the rat pituitary cell line, GH3, and to the hair cells dissociated from a chick vestibular organ. In both preparations, Ca channels were gated open by depolarizing command pulses and were not inactivated. The activation kinetics were reasonably fitted by the mm2 kinetic model, while the steady-state noise analysis indicated a presence of much faster opening-closing kinetics in the gating mechanism. The fast opening-closing gating mechanism was observed in the Ba cullents passing through a single Ca channel. Steady-state noise analyses and single channel Ba currents suggest a presence of dual gates in the Ca channel; the one may be a voltage dependent slow gate which operates on a reaction scheme analogous to the mm2 process, and the other may be a less voltage dependent fast gate which seems operating independent of the slow gate.
The intracellular DNA of bacteria, bacteriophage and plasmids is subject to topological constraints that function to maintain it in a superhelical conformation. For the last several years, accumulating evidence has indicated that supercoiling of DNA duplex is required for effective transcription, as well as for the replication and recombination of cellular DNA. The relevance of DNA superhehlicity to transcription in vivo has been suggested by the observations that the overall rate of transcription directed by the E. coli, bacteriophage and plasmid genomes is generally reduced when the activity of DNA gyrase is inhibited by the specific drugs, such as nalidixic acid or coumermycin. An interesting observation from our in vitro studies has been that stimulation of transcription by superhelicity of DNA is more pronounced with S 100 crude extract proteins than with pure RNA polymerase. DNA in the prokayrotic cell has a compact conformation due to its interaction with cellular proteins (Histone like proteins). Recentry, seven classes of those proteins (HLP I, HLP II, 28K protein etc.) have been isolated and characterized as essential components of the nucleoid. In this review, we focus on the effect of superhelical conformation of the DNA duplex and association of the DNA with the nucleoid proteins on transcription.
In order to mimic the function of cytochrome oxidase and inversely to get insight into its function and structure and furthermore their correlation, electrocatalytic reduction of molecular oxygen was examined using water-soluble and immobilized iron and cobalt porphyrins and phthalocyanines. In the presence of iron porphyrins, oxygen was reduced via hydrogen peroxide to water quantitatively by an electrogenerated penta-coordinated high-spin iron (II) form of the porphyrins at potentials closely correlated with iron (III) to iron (II) reduction potentials. The rate constant of oxygen reduction in natural enzyme system was attained only by the use of porphyrins containing a lot of amino groups, suggesting inversely one of the causes of high composition ratio of basic amino acids in this enzyme. By the use of iron phthalocyanines also, oxygen was reduced via hydrogen peroxide to water at potentials correlated with iron (II) to iron (I) reduction potentials. Howerver when mononuclear cobalt complexes were employed, hydrogen peroxide was produced almost quantitatively as the final product.