Fig. 1.

Potential mechanisms of PglC, a prototypic dual domain PGT. (A) The sequential mechanism involves formation of a noncovalent ternary complex featuring both substrates. (B) The ping-pong mechanism involves reaction of an active-site nucleophile with the α-phosphate of the NDP-sugar substrate in step 1 to generate a covalent enzyme-substrate intermediate with release of UMP. In step 2, the covalent enzyme intermediate undergoes nucleophilic attack by the second substrate to generate the product. [ENZ-NU represents a reactive nucleophilic functional group (NU) as part of the enzyme (ENZ) active site.]