Isolation of lecanoric acid, an inhibitor of histidine decarboxylase from a fungus.

A method of determining histidine decarboxylase activity was established. In this method, 14C-histamine was separated from 14C-histidine by Amberlite CG-resin column in the ammonium form. Lecanoric acid was obtained by screening histidinedecarboxylase inhibitors produced by microorganisms. It is the first isolation of this compound from fungi. The inhibition by lecanoric acid was competitive with histidine and noncompetitive with pyridoxal phosphate. Lecanoric acid did not inhibit aromatic amino acid decarboxylase. Though lecanoric acid was hydrolyzed easily both in vivo and in vitro, its structure yielded an information useful in developing histidine decarboxylase inhibitors of a new structural type.