    3.2.1.179 | beta-D-4-deoxy-Delta4-GlcAp-(1->4)-beta-D-Glcp-(1->4)-alpha-L-Rhap-(1->3)-D-Glcp + H2O = 5-dehydro-4-deoxy-D-glucuronate + beta-D-Glcp-(1->4)-alpha-L-Rhap-(1->3)-D-Glcp |
the enzyme triggers a hydration reaction acting on the C-C double bond between the C-4 and C-5 positions of the unsaturated uronic acid residue in GAG disaccharide using the catalytic Asp residue (Asp-II) as a general acid and base catalyst to protonate the C-4 atom of unsaturated uronic acid residue and to deprotonate the water molecule. The deprotonated water molecule attacks the C-5 atom of the unsaturated uronic acid residue to yield unstable hemiketal, followed by its spontaneous conversion to 4-deoxy-L-threo-5-hexosulose-uronic acid and an amino sugar via hemiacetal formation and cleavage of the glycoside bond |
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