title: Assay for tyrosine hydroxylase in hypothalamic homogenates using high-performance liquid chromatography with electrochemical detection.
abstract: A highly sensitive and reliable assay for tyrosine hydroxylase (TH) activity in hypothalamic homogenates of male rats using high-performance liquid chromatography with electrochemical detection is described. Modification of sample preparation and chromatographic conditions led to a complete separation of L-3,4-dihydroxyphenylalanine (L-DOPA) and alpha-methyldopa from all interfering catecholamines and their metabolites. This assay is highly sensitive; 2 pmol of L-DOPA formed enzymatically could be measured. We were able to determine TH activity in tissue pieces weighing less than 1 mg. TH activity was not changed after storage for three months at -80 degrees C. In hypothalamic homogenates the Michaelis constant (KM) for L-tyrosine was 80.5 +/- 6.5 mumol/l and the maximal velocity (Vmax) was 132.5 +/- 10.5 pmol/mg of protein per min for L-DOPA formed enzymatically.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004563:Electrochemistry; D007031:Hypothalamus / Q000201:enzymology*; D007202:Indicators and Reagents; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis*
chemical_list: D007202:Indicators and Reagents; D004295:Dihydroxyphenylalanine; D014446:Tyrosine 3-Monooxygenase