Brain tyrosine hydroxylase: kinetic properties and regulation of the activity.

Electrical stimulation of rat hypothalamic synaptosome suspensions produced activation of tyrosine hydroxylase due to increase of the affinity for tyrosine and 6,7-dimethyl-5,6,7,8-tetrahydropterine cofactor, decrease of the affinity for dopamine and enhancement of substrate inhibition. Cocaine (10(-7) - 10(-5) M) in vitro caused enzyme activation; when administered to animals systemically (0.5 mg/kg) the drug produced inhibition of hypothalamic tyrosine hydroxylase probably through a receptor-mediated feedback mechanism.