Phosphoglucomutase isolation

Phosphoglucomutase was isolated by the Coris and crystallized by Najjar. Its mechanism of action was suggested from experiments by Leloir in 1951 using [32P]. The enzyme is a phosphoprotein. Leloir showed that the phosphate group was transferred from the enzyme to G-1-P in the course of the reaction to give G-1,6 diP, which then donated the phosphate from its 1-position back to the enzyme, releasing G-6-P ... 

The phosphoglucomutase enzyme catalyzes reaction 79. Reaction 78, which involves an inversion (Walden inversion) at C4 of the hexose, was shown to require a heat-stable cofactor. s This coenzyme for the galactowaldenase system was isolated and its structure determined. The coenzyme is uridinidiphosphoglucose (UDPGlucose). 

A recent search for this enzyme and coenzyme have revealed that phosphoglucomutase itself may be the phosphoribomutase, since the crystalline enzyme appears to be active on both substrates in a constant ratio maintained through intermediate stages in the purification. In the presence of trace amounts of glucose-1,6-diphosphate, ribose-1,5-diphosphate appears to be generated, and a compound which is probably this latter substance has been isolated from the reaction mixture. 

Overexpression of selected enzymes involved in galactose biosynthesis, either independently or collectively as an entire metabolic pathway, may be a route to increased levels of galactosylation in CHO cells. These include the UDP-glucose-4-epimerase [36], the phosphoglucomutase [43], and the UDP-glucose pyrophosphor-ylase [44] and the UDP-galactose transferase [45]. All of the genes for these enzymes have been isolated from either mammalian or microbial sources. 

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