Methionine and cysteine metabolism in Fasciola hepatica.

Radiolabel from the methyl groups of serine and methyltetrahydrofolate was readily incorporated into methionine in adult Fasciola hepatica, and a substantial proportion of the label from [35S]methionine appeared in cysteine. The data suggest that methionine synthesis is via methyltetrahydrofolate-homocysteine methyltransferase and that there is cysteine synthesis from methionine. Cystathionine-beta-synthase and gamma-cystathionase activities were demonstrated in homogenates.