its properties have been studied , most of them on an intermediate fraction of the purification , because of the instability of the purified enzyme in spite of the addition of different stabilizing agents : the enzyme decarboxylates 5-hydroxytryptophan ( 5 htp ) and dopa in a ratio constant throughout the purification but does not decarboxylate tryptophan , tyrosine , histidine at a measurable rate .
C0000578
5
C0041249
tryptophan