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Title
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Refined 2.5 A structure of murine adenosine deaminase at pH 6.0.
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Authors
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A.J.Sharff,
D.K.Wilson,
Z.Chang,
F.A.Quiocho.
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Ref.
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J Mol Biol, 1992,
226,
917-921.
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PubMed id
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Abstract
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The X-ray structure of murine adenosine deaminase complexed with the
transition-state analogue 6-hydroxyl-1,6-dihydropurine ribonucleoside has been
determined from a single crystal grown at pH 4.2 and transferred to mother
liquor of increasing pH up to a final pH of 6.0 prior to data collection. The
structure has been refined to 2.5 A to a final crystallographic R-factor of 20%
using phases from the previously refined 2.4 A structure at pH 4.2. Kinetic
measurements show that the enzyme is only 20% active at pH 4.2 whereas it is
fully active between pH 6.0 and pH 8.5. The refined structures at either pH are
essentially the same. Consideration of the pKa values of the key catalytic
residues and the mechanism proposed on the basis of the structure suggests that
the ionization state of these residues is largely responsible for the pH
dependence on activity.
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