1961 年 81 巻 12 号 p. 1754-1761
Following the previous work on biological changes of nicotinic acid N-oxide in a rat, in which about one-half of the compound was found to be reduced to nicotinic acid, perfusion test with excised liver was carried out and only a few percentages of nicotinic acid N-oxide was found to have been reduced in rabbit and entirely unchanged in a rat liver.
Enzymatic examination of in vitro reduction of nicotinic acid N-oxide was made and following points were clarified as the mechanism of the reduction system.
When using liver as the enzyme source, the main enzyme protein was present in the supernatant of cell fraction by the Schneider method and specific activity increased about two-fold by ammonium sulfate fractionation (0.28-0.50 saturation). Besides this protein, there is activation action in the proteinic factor originating from mitochondria. A low-molecular activation substance is necessary as a co-factor and, as far as the present examinations are concerned, ATP and ADP are most effective, followed by DPN and DPNH. Both the oxidation and reduction forms of TPN were devoid of this activity.
It is interesting to note that ATP and ADP take part in the reduction reaction and that AMP and adenine have strong inhibitory action in a system using ATP as the activator. However, it was not possible to clarify the mechanism of this reaction.