Effect of Ascorbic Acid on Hydroxylase Activity: I. Stimulation of Tyrosine Hydroxylase and Tryptophan-5-Hydroxylase Activities by Ascorbic Acid

The effect of ascorbic acid on the hydroxylase and dehydrogenase activities was studied in vivo to clarify its role in the biological oxidation. Tyrosine hydroxylase and tryptophan-5-hydroxylase which require 2-amino-4-hydroxy-6, 7-dimethyltetrahydropteridine (DMPH4), NADP and molecular oxygen were investigated with the non-scorbutic and scorbutic guinea pigs. Several dehydrogenases such as glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase and malic enzyme, which require no molecular oxygen but NADP, were also studied by comparing the activities in the non-scorbutic guinea pig with those in the scorbutic guinea pig. The results indicated that the activities of tyrosine hydroxylase and tryptophan-5-hydroxylase of the adrenal gland, liver and brain of the nonscorbutic guinea pig were higher than the values found in the scorbutic guinea pig, although no significant change in the activity of dehydrogenase was observed in the tissues of the non-scorbutic and scorbutic guinea pigs.