Schistosoma mansoni: Decarboxylation of 5-hydroxytryptophan, l-dopa, and l-histidine in adult and larval schistosomes

Abstract

Homogenates of adult and larval Schistosoma mansoni, decarboxylate 5-hydroxytryptophan (5-HTP) and l-dopa in vitro, but not l-histidine. The enzyme responsible, similar to mammalian aromatic- l-amino acid carboxy-lyase (EC 4.1.1.28), has a K m of 5.1 × 10 −5 M, a V max of 1.1 nmole/30 min/mg protein, and high activity at pH 7.9. No evidence for a specific l-histidine decarboxylase (EC 4.1.1.22) was found in either stage of the schistosome. In vivo, schistosomules form serotonin from 5-HTP, detectable by thin-layer chromatography, within 3–4 hr after addition of 14C-labeled 5-HTP to the medium. Addition of 14C-labeled tryptophan under similar conditions results in no detectable formation of 5-HTP.