Formation of circular polyribosomes in wheat germ cell-free protein synthesis system |
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Authors: | Madin Kairat Sawasaki Tatsuya Kamura Nami Takai Kazuyuki Ogasawara Tomio Yazaki Kazumori Takei Toshiaki Miura Kin-Ichiro Endo Yaeta |
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Institution: | Department of Biomedicine, Division for Anatomy and Cell Biology, University of Bergen, Jonas Lies vei 91, N-5009 Bergen, Norway. |
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Abstract: | 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. |
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