because hydroxylation of tyrosine to dopa and of tryptophan to 5-hydroxytryptophan may require the same cofactor and pterin reductase as phenylalanine hydroxylase , these mutants may also prove useful for the study of the role of catecholamines and serotonin , substances known to be present in tetrahymena .
C0013023
dopa
C0007412
catecholamines