Abstract
Bovine adrenal tyrosine hydroxylase (TH) is isolated in a partially inhibited state with the feed-back inhibitors adrenaline and noradrenaline tightly coordinated to high-spin (S = 5 2 ) Fe(III) at the active site. In addition to the charge-transfer interaction with iron, an additional charged group in the polypeptide chain, with an apparent p K a of about 5.3 at 4°C, is involved in the binding of catecholamines. Protonation of this group increases the pseudo-first order rate constant for the dissociation of the TH-[ 3H]noradrenaline complex more than 100-fold at 4°C. At pH 7.0 and 30°C, phosphorylation of Ser-40 causes a 6-fold increase in the rate constant for this dissociation.
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