URIDINE 5'-DIPHOSPHATE-GLUCOSE DEHYDROGENASE FROM SOYBEAN NODULES

A highly purified preparation of uridine 5'-diphosphate (UDP)-glucose (Glc) dehydrogenase (DH; EC 1.1.1.22) has been characterized from soyb ean (Glycine max L.) nodules. The enzyme had native and subunit molecu lar masses of approximately 272 and 50 kD, respectively. UDP-Glc DH di splayed typical hyperbolic substrate kinetics and had K-m values for U DP-Glc and NAD(+) of 0.05 and 0.12 mM, respectively. Thymidine 5'-diph osphate-Glc and UDP-galactose could replace UDP-Glc as the sugar nucle otide substrate to some extent, but the enzyme had no activity with NA DP(+). Soybean nodule UDP-Glc DH was labile in the absence of NAD(+) a nd was inhibited by a heat-stable, low-molecular-mass solute in crude extracts of soybean nodules. UDP-Glc DH was also isolated from develop ing soybean seeds and shoots of 5-d-old wheat and canola seedlings and was shown to have similar affinities for UDP-Glc and NAD(+) as those of the soybean nodule enzyme. UDP-Glc DH from all of these sources was most active in young, rapidly growing tissues.