PROPERTIES OF TYROSINE HYDROXYLASE

Abstract

This chapter discusses a study examining properties of tyrosine hydroxylase. Tyrosine hydroxylase was isolated from the adrenal gland and brain, the enzyme was originally described as particle bound; the fraction of tyrosine hydroxylase which was found in the supernatant was considered to have been solubilized by the prolonged homogenization. In the course of efforts to purify the enzyme, it was found that the enzyme from bovine adrenal glands has the tendency to precipitate; in contrast, the rat adrenal enzyme was found exclusively in soluble form, and it does not precipitate. These observations suggested that perhaps tyrosine hydroxylase was a soluble enzyme, and that in certain species it has the tendency to precipitate and to appear as particle-bound. To test this hypothesis, the subcellular distribution of bovine tyrosine hydroxylase was studied, using procedures specifically designed for sub-cellular fractionation of enzymes. The sub-cellular distribution of tyrosine hydroxylase was studied using different homogenization media, differential centrifugation, and sucrose density gradient fractionation. The results indicated that tyrosine hydroxylase is a soluble enzyme; most of the tyrosine hydroxylase (64%) remains at the top of the gradient, and only a very small fraction (10%) is associated with the chromaffin granules.