5-Hydroxylation of tryptophan

The hydroxylation of tyrosine into dopa is catalysed by tyrosinase, that of tryptophane into 5-hydroxytryptophane is probably catalysed by a specific tryptophane-5-hydroxylase but other workers were not able to isolate the latter from the mucosa of the small intestine in rats and guine2i-pigs/ " But recently it was possible by means of isotope techniques to demonstrate tryptophanehydroxylase in carcinoid tissue as well as in human platelets. (1864) 5-Hydroxylation of tryptophane seems to be the rate-limiting step in the synthesis of serotonin. Tryptophanehydroxylase is strongly inhibited in vivo by / -chlorophenylalanine. Initial therapeutic trials with the called drug in carcinoid patients resulted in a marked improvement of intestinal symptoms but did not prevent the attacks of flushing. ... 

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