In the present investigation comparison of the activity of oxidoreductases (succinate-ferricyanide reductase, cytochrome c-ferricyanide reductase, NADH-ferricyanide reductase, NADPH-ferricyanide reductase and peroxidase), citrate synthase and alkaline phosphatase in various tissues (cerebrum. cerebellum, cardiac muscle, liver and kidney) was made ultracytochemically between normal male adult rats kept in the ordinary light environment and those kept in the complete dark.
It was found that all oxidoreductases examined except peroxidase revealed the higher activity in rats kept in the complete dark in terms of the number of the enzymatically positive mitochondria and the activity of each mitochondrion. This tendency was most evident in the case of the NADPH-ferricyanide reductase; the NADPH-ferricyanide reductase activity was hardly detectable in tissues of rats kept in the ordinary light environment, but it could easily be detected in tissues of rats kept in the complete dark.
This increase of the enzymatic activity (diurnal change) was not manifested in rats kept in the dark for 1hr, but began to be manifested 3 to 5 hrs following the onset of keeping rats in the complete dark, when examined with the NADPH-ferricyanide reductase activity.
Puromycin (2.5mg/100g of body weight) and actinomycin D (0.06mg/100g of body weight) did not affect the occurrence of this diurnal enzyme change, suggesting that the diurnal enzyme change is the increase in the activity of mitochondrial oxidoreductases rather than the induction of enzymes (new synthesis of enzyme proteins).
The diurnal change was not found with alkaline phosphatase and peroxidase, but it was of interest to note that the activity of citrate synthase seemed to be slightly lower in rats kept in the dark for 24hrs.