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K Yoshihara

Publications and source records attributed to K Yoshihara.

14 recordsLinked to original sources
PubMed1978

Bovine thymus poly(adenosine diphosphate ribose) polymerase.

About 1,300-fold purification of poly(adenosine diphosphate ribose) polymerase has been achieved from the extract of bovine thymus with a recovery of 10 to 20%. The final preparation has a purity of 99%, and the enzyme is composed of a single peptide with a molecular weight of 130,000. The purified enzyme required NAD+, Mg2+, a thiol compound, DNA, and histones for full activity. Whereas DNA is essential for activation of the enzyme, histones are not. The observed stimulation of the reaction by histones is shown to be due to masking of the inhibitory effect of contaminating denartured DNA in native DNA preparation. The concentration of DNA required for half-maximal enzyme activity (apparent Km for DNA) is proportional to the concentration of enzyme in the reaction mixture. The minimum estimation of the number of nucleotide pairs of DNA required for half-maximal activation of one enzyme molecule is 220 to 240 for bulk of calf thymus DNA, while the value is 10 for a calf thymus DNA fraction, "active DNA," which was separated from the enzyme fraction in a stage of the purification. These results suggest that the enzyme is activated by binding to a specific site on calf thymus DNA. The apparent Km for NAD+ and the maximum velocity of the enzyme are estimated to be 60 micrometer and 0.91 mumolper min per mg, respectively.

Animals↗
PubMed1976

A possible mode of cardiovascular actions of dopamine in dogs.

A possible mode of cardiovascular actions of dopamine was studied using ephedrine. In the dog pretreated with repeated administrations of ephedrine (total dose, 40 or 80 mg/kg, i.v.) or with combined administrations of ephedrine (total dose, 90 mg/kg, s.c. and i.v.) and reserpine (2 mg/kg, s.c., 24 hr previously), pressor responses to dopamine were eliminated and reversed to depressor responses whereas depressor responses to dopamine were potentiated. Positive chronotropic effects of dopamine were almost eliminated. Pressor and positive chronotropic effects of tyramine were almost abolished. Sympathomimetic effect of noradrenaline and adrenaline were potentiated while those of isoprenaline were inhibited. In the heart-lung preparation of ephedrine-treated dogs (total dose, 40 mg/kg, i.v.), cardiac stimulating effects of dopamine and tyramine were strongly depressed, and those of noradrenaline, adrenaline and isoprenaline were reduced to some extent. In the open-chest dogs, after pretreatment of cocaine (4 mg/kg, i.v.), pressor, positive inotropic and chronotropic effects of noradrenaline were potentiated, whilst those of tyramine were inhibited. Those of dopamine were not visibly altered, but depressor, negative chronotropic and inotropic effects of dopamine appeared at small doses. In the ephedrine-pretreated dogs, these sympathomimetic effects of dopamine and tyramine after cocaine were strongly depressed and those of noradrenaline were inhibited to a certain degree. The results obtained with ephedrine suggest that dopamine differs from other catecholamines and tyramine in the mode of cardiovascular actions.

Animals↗
PubMed1975

Evidence for adenosine diphosphate ribosylation of Ca2+, Mg2+-dependent endonuclease.

The molecular basis for the inhibition of the Ca2+,Mg2+-dependent endonuclease resulting from the formation of poly(adenosine diphosphate ribose) (ADP-Rib) was studies in a simplified system containing purified rat liver or bull semen endonuclease, purified rat liver poly(ADP-Rib) synthetase, [3H]NAD+, and DNA. Poly-(adp-rib) synthetase activity was stimulated when Ca2+, Mg2+-dependent endonuclease was added to the reaction mixture in place of histones, suggesting that the endonuclease can act as an acceptor for ADP-Rib. Evidence was presented to show that the ADP-Rib moiety of [3H]NAD+ was incorporated in the endonuclease fraction. The [3H]ADP-Rib bound to the endonuclease was in the form of monomers and oligomers and not long chain polymers. The present results suggest that the Ca2+,Mg2+-dependent endonuclease was ADP-ribosylated when the endonuclease was incubated with poly(ADP-Rib) synthetase and NAD+.

Adenosine Diphosphate↗