Abstract
1. 1. UDPG dehydrogenase (UDPG: NAD oxidoreductase, EC 1.1.1.22), was purified 88-fold to a specific activity of 2.3 from a derepressed strain of Escherichia coli. 2. 2. The enzyme has a molecular weight of approximately 86 000 and a pH optimum of 9.0; K m is 1.0 mM for UDPG and 0.05 mM for NAD, respectively. 3. 3. UDPG, CDPGlc and dTDPGlc, but not GDPGlc or ADPGlc function as substrates. 3-Acetylpyridine adenine dinucleotide, 3-pyridinealdehydeadenine dinucleotide, thionicotinamide adenine dinucleotide, deamino adenine dinucleotide and 3-acetylpyridine deamino adenine dinucleotide, but not 3-pyridinealdehyde deaminoadenosine dinucleotide, are cosubstrates. 4. 4. The enzyme is stable for 2 months when frozen at −4 °C in the presence of UDPG. UDPG and 2-mercaptoethanol are necessary for optimal enzyme activity. 5. 5. UDPXyl is an inhibitor strictly competitive with UDPG and noncompetitive with NAD; NADH is an inhibitor strictly competitive with NAD and uncompetitive with UDPG. UDPglucuronate is an inhibitor competitive with UDPG at high UDPG concentrations; at low UDPG concentrations UDPglucuronate is an inhibitor which displays positive cooperativity.
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