Tyrosine Hydroxylase Activity in Rat Brain Synaptosomes: Direct Measurement Using High Performance Liquid Chromatography

Abstract
By use of high performance liquid chromatography with electrochemical detection to measure dopamine production, tyrosine hydroxylase (EC 1.14.16.2) activity was measured in rat brain synaptosomes from striatum and forebrain. Normal specific activities 3- to 5-fold higher than previously reported in the literature for radiochemical methods of assay were found. Synaptosomes may contain a significant amount of endogenous substrate for tyrosine hydroxylase, which causes dilution of the added labeled tyrosine and underestimation of the activity of this enzyme when radiochemical methods are used.