UGGPase catalyzes the synthesis of UDP-Glucose/UDP-Galactose.
UGGPase: UDP-Galactose/Glucose Pyrophosphorylase catalyzes the reversible production of UDP-Glucose/UDP-Galactose and pyrophosphate (PPi) from Glucose-1-phosphate/Galactose-1-phosphate and UTP. Its dual substrate specificity distinguishes it from the single substrate enzyme UDP-glucose pyrophosphorylase. It may play a key role in the galactose metabolism in raffinose oligosaccharide (RFO) metabolizing plants. RFO raffinose is a major photoassimilate and is a galactosylderivative of sucrose (Suc) containing a galactose (Gal) moiety. Upon arriving at the sink tissue, the Gal moieties of the RFOs are initially removed by alpha-galactosidase and then are phosphorylated to Gal-1-P. Gal-1-P is converted to UDP-Gal. The UDP-Gal is further metabolized to UDP-Glc via an epimerase reaction. The UDP-Glc can be directly utilized in cell wall metabolism or in Suc synthesis. However, for the Suc synthesis UDP-Glc must be further metabolized to Glc-1-P. This can be carried out either by the UGPase in the reverse direction or by the dual substrate PPase itself operating in the reverse direction. According to the latter possibility, the three-step pathway of Gal-1-P to Glc-1-P could be carried out by a single PPase, functioning sequentially in reverse directions separated by the epimerase reaction.
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