although phenylalanine hydroxylase utilizes 6-me-pdh4 ( km = 0.15 mm ) , the maximum velocity of tyrosine production is 20 times slower than that with 6-me-ph4 , indicating that a ring opening reaction is not a rate-limiting step in the hydroxylase pathway .
C0031456
phenylalanine hydroxylase
C0020364
hydroxylase