Enzymatic decarboxylation of L-threo-3,4-dihydroxyphenylserine in rat heart.

Decarboxylation of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) by the higher speed supernatant of the rat heart homogenate and the regional distribution of L-threo-DOPS decarboxylase activity were examined. Decarboxylation was demonstrated to occur specifically with L-isomer but not with D-isomer. Addition of pyrogallol was necessary for maximal recovery of norepinephrine. The optimal condition for decarboxylation of L-threo-DOPS by the rat heart enzyme was similar to conditions required with the enzymes from brain and kidney. Under the optimal conditions, Km and Vmax for L-threo-DOPS were 2.1 mM and 6.4 nmoles/mg protein/15 min, respectively. Decarboxylation of L-threo-DOPS was markedly inhibited by D-threo-DOPS and D-DOPA. The L-aromatic amino acid decarboxylase activity was highest in the right auricle followed by the atrial body, the left auricle, the right ventricle and the left ventricle.