Effect of ascorbic acid on tyrosine hydroxylase activity in vivo

The activity of tyrosine hydroxylase in the homogenate of adrenal gland decreased in scurvy, and it was recovered by the administration of ascorbic acid. The mechanism of increase in tyrosine hydroxylase activity by administration of ascorbic acid has been studied. The enzyme activities of the adrenal homogenates in nonscorbutic and scorbutic guinea pigs were changed neither by dialysis nor by gel filtration on Sephadex G-25. However, stimulation of enzyme activity by the administration of ascorbic acid, was blocked either by puromycin or by actinomycin D. Tyrosine hydroxylase was purified by ammonium sulfate fractionation, Sephadex G-200, and hydroxylapatite chromatography. Antibody to the partially purified enzyme was prepared in rabbit. Immunochemical analysis indicated that there was a constant amount of immunochemically precipitable enzyme per unit of enzyme activity. The studies reported here showed that the increase of enzyme activity by the administration of ascorbic acid was due to the increased amount of the enzyme protein.