Tryptophan Hydroxylation: Measurement in Pineal Gland, Brainstem, and Carcinoid Tumor

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Science  13 Jan 1967:
Vol. 155, Issue 3759, pp. 217-219
DOI: 10.1126/science.155.3759.217


Development of a rapid and sensitive radioassay has permitted study of the conversion of tryptophan to 5-hydroxytryptophan in mammalian tissues. Of normal tissues examined, beef and rat pineal gland contained the highest activity. This is the first direct demonstration of tryptophan hydroxylase in this hydroxyindole-rich tissue. Rat and rabbit brainstem and human carcinoid tumor also had quantities of enzyme that could be measured easily. The reaction requires a reduced pteridine and oxygen and is inhibired by Para-Chorophenylalanine.