TDPG-oxidoreductase

It is well established that oxygen in the presence of platinum (Adams catalyst) can achieve specific oxidation of secondary alcohols by a preferential attack upon hydrogen in an equatorial position (25). Catalytic oxidation of methyl a- and /3-D-galactopyranoside (26), fallowed by catalytic reduction with hydrogen, led to the formation of methyl a- and /3-6-deoxy-D-galactopyranoside (D-fuco-pyranoside) in 15% and 35% yield, respectively. This oxidation-reduction sequence with selective oxidation at carbon 4 as the initial step is structurally closely related to the above described pathway for TDPG-oxidoreductase. 

Another important property of TDPG-oxidoreductase is its reversible dissociation with enzyme bound-NAD+ (30,31). Treatment of the enzyme with p-chloromercuriphenylsulfonate results in the release of enzyme bound NAD+ and formation of two protein subunits. Incubation of these inactive subunits with cysteine and excess NAD+ leads to reassociation of the subunits and complete return of enzymatic activity. Conditions for the isolation of the subunits of molecular weight of about 40,000 were described by Zarkowsky et al. (32). 

Table II. Summary of Isotope Effect Data for TDPG-Oxidoreductase and UDP Galactose-4-Epimerase (40)°...

Table III. Comparison of TDPG-Oxidoreductase (28, 30, 31, 32) and UDP-Galactose-4-Epimerase (38, 40, 41, 42, 43) from E. Colt B...

A summary of some of the common features for the first three reactions described in this preparation, TDPG-oxidoreductase, UDP-galac-tose-4-epimerase, and UDP-glucuronic acid carboxylase, are shown in Figure 14. Our initial discussion is restricted to these three examples since we have more information about them. 

Figure 14. Common features of the TDPG-oxidoreductase, UDP-galactose-4-epimerase, and UDP-glucuronic acid carboxylase...

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