Wikipedia states that Tyrosine Hydroxylase "is increased acutely (minutes) by phosphorylation and chronically (days) by protein synthesis. ... The phosphorylation can be sustained by nicotine for up to 48 hours."
"Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine (DOPA). . . . It does so using tetrahydrobiopterin as a coenzyme. DOPA is a precursor for dopamine, "
http://en.wikipedia.org/wiki/Tyrosine_hydroxylase
John