Nucleotide Inhibition of Glyoxalase II Page: 21
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indicate that the enzyme has two free sulfhydryl groups per monomer, four in total for the
mammalian dimer and two for the yeast enzyme (93).
Modification of two arginine residues by specific reagents also causes complete
loss of catalytic activity (144). The addition of substrate provides effective protection
against the loss of activity by preventing the modification of one of the affected arginine
residues (144). Results have been interpreted as indicating the presence of an active site
arginine essential for catalytic activity.
Modification of Glo-I by tryptophan specific reagents also causes complete
inactivation of the enzyme activity (145, 146). One study indicated that a total of three
tryptophan residues are modified, the addition of substrate protects the enzyme from
modification, and the loss of activity result from the modification of only one of the
tryptophan residues (145). Results were interpreted as indicating the presence of an
active site tryptophan essential for catalytic activity.
The nitration of tyrosine residues also causes complete inactivation of the enzyme
(146). The addition of substrate provides effective protection against the loss of activity
(146). It is not yet clear whether the residue modified is involved with the binding of
substrate or the coordination of the zinc ion (117).
Other studies have shown that the metal ion is located near the active site (116,
120). Although the presence of a metal ion is required for catalysis, the ability of the
mammalian enzyme to accept a number of metal ions while remaining enzymatically
active indicates that the role of the metal ion may be to provide structural integrity to the
protein.21
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Gillis, Glen S. Nucleotide Inhibition of Glyoxalase II, dissertation, May 1999; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc2183/m1/30/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .