Nucleotide Inhibition of Glyoxalase II Page: 45
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In order to ascertain the efficiency of the glyoxalase system in the removal of
methylglyoxal from cells, as well as determine if any unknown kinetic factors are
involved in the conversion of methylglyoxal to D-lactate, quantitative models of the
pathway have been developed (186, 189, 223). To date, all studies indicate that the steady
state concentrations of the substrates for the glyoxalase enzymes in vivo are maintained at
subsaturating levels (<< KM values reported for that enzyme) (110, 186, 187, 189, 223).
Therefore, results from in vitro studies have been used to propose a model for the
metabolic flux through the system under conditions in which substrate concentrations are
much lower than the KM values for the two enzymes (186, 189, 223).
Under these conditions, the overall rate of the conversion of methylglyoxal to D-
lactic acid is thought to be limited by the rate of formation of the hemithioacetal substrate
for Glo-I (186). This interpretation was obtained from calculations based upon free
energy diagrams derived from apparent rate constants for each of the reactions that occur
within the glyoxalase system (186). The concentration of GSH in tissues is generally
maintained at concentrations high enough to be kinetically unimportant in the reaction
(186). Therefore, the formation of the hemithioacetal is then predicted to be dependent
upon the concentration of free methylglyoxal; the flux through the system is thus under
substrate level control.
Both of the glyoxalase enzymes in their purified state appear to act at near optimal
catalytic efficiency (189, 223). Values for kcat / KM
(3.5 * 106 M-1 S-1 for yeast Glo-I, 8.8 * 105 M 1 1 for rat erythrocyte Glo-II, at pH 7,
250C) approach the estimated upper limits for such values (224). By the application of
the viscogenic variation method to kinetic studies, both enzymes have been demonstrated45
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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/m1/54/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .