5- Hydroxytryptophan assay

Aromatic L-amino acid decarboxylase catalyzes the decarboxylation of l-5-hydroxytryptophan (l-5-HTP) to serotonin (5-HT). In the assay, l-5-HTP was used as the substrate and the formation of 5-HT was measured. 

Decarboxylation of L-3,4-dihydroxyphenylalanine to dopamine, and of 5-hydroxytryptophan to serotonin, is catalyzed by aromatic L-amino acid decarboxylase. A single enzyme may be responsible for both activities. This assay permits simultaneous determination of both activities. 

With the rediscovery of Landsteiner s observations that even very small molecules could be rendered immunogenic by linking them covalently to a protein, it became possible to develop immunoassays for almost every molecule of clinical interest. The main medical application of immunoassays remained in endocrinology, producing a revolution in clinical practice by facilitating the detection and quantitation of steroids (such as aldosterone and cortisol) and of hormones derived by the biotransformation of single amino acids and fatty acids (such as thyroxine, melatonin, and 5-hydroxytryptophan). Not only is it possible to measure these hormones at the infinitesimally low concentrations at which they naturally occur in tissues, plasma, and other body fluids, but the assays are sufficiently rapid and economical to be useful in day-to-day patient care. 

This is a pyridoxal phosphate protein which catalyses the synthesis of serotonin. It may be assayed radiochemically using DL-5-hydroxytryptophan-l- C [447]. 

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