TYROSINE-HYDROXYLASE ASSAY FOR DETECTION OF LOW-LEVELS OF ENZYME-ACTIVITY IN PERIPHERAL-TISSUES

A nonisotopic assay for tyrosine hydroxylase, with optimized signal-to -noise ratios, enables determination of low levels of enzyme activity in peripheral tissues, DOPA produced by the enzyme is measured using H PLC with electrochemical detection, Increased signal-to-noise ratios a re obtained by including in the reaction mixture glycerol for reductio n of blank values and dihydropteridine reductase and NADPH for regener ation of the tetrahydropteridine cofactor. With this method, tyrosine hydroxylase activity can be detected in as few as 200 PC12 cells and i n peripheral tissues at levels as low as 4.5 fmol/min/mg wet weight. T he assay permits activity to be assessed in a variety of peripheral ti ssues.