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Different stabilities and denaturation pathways for structurally related aromatic amino acid hydroxylases
Author(s) -
Kleppe Rune,
Haavik Jan
Publication year - 2004
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2004.03.092
Subject(s) - chemistry , aromatic amino acids , urea , tryptophan , denaturation (fissile materials) , phenylalanine hydroxylase , phenylalanine , amino acid , tyrosine , enzyme , biochemistry , tryptophan hydroxylase , stereochemistry , nuclear chemistry , receptor , serotonergic , serotonin
We have compared the urea stability of the human aromatic amino acid hydroxylases (AAAHs), key enzymes involved in neurotransmitter biosynthesis and amino acid homeostasis. Tyrosine‐, tryptophan‐ and phenylalanine hydroxylase (TH, TPH and PAH, respectively) were transiently activated at low urea concentrations and rapidly inactivated in >3 M urea. The denaturation of TH occurred through two cooperative transitions, with denaturation midpoints of 1.41 ± 0.06 and 5.13 ± 0.05 M urea, respectively. Partially denatured human TH (hTH) retained more of its secondary structure than human PAH (hPAH), and was found to exist as tetramers, whereas hPAH dissociated into dimers. Furthermore, the urea‐induced aggregation of hPAH was 100‐fold higher than for hTH. These results suggest that the denatured state properties of the AAAHs contribute significantly to the stability of these enzymes and their tolerance towards missense mutations.