Isoforms of glucose 6-phosphate dehydrogenase in Deinococcus radiophilus.
Glucose 6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in Deinococcus radiophilus, an extraordinarily UV-resistant bacterium, was investigated to gain insight into its resistance as it was shown to be involved in a scavenging system of superoxide (O2-1) and peroxide (O2-2) generated by UV and oxidative stresses. D. radiophilus possesses two G6PDH isoforms: G6PDH-1 and G6PDH-2, both showing dual coenzyme specificity for NAD and NADP. Both enzymes were detected throughout the growth phase; however, the substantial increase in G6PDH-1 observed at stationary phase or as the results of external oxidative stress indicates that this enzyme is inducible under stressful environmental conditions. The G6PDH-1 and G6PDH-2 were purified 122- and 44-fold (using NADP as cofactor), respectively. The purified G6PDH-1 and G6PDH-2 had the specific activity of 2,890 and 1,033 U/mg protein (using NADP as cofactor) and 3,078 and 1,076 U/mg protein (using NAD as cofactor), respectively. The isoforms also evidenced distinct structures; G6PDH-1 was a tetramer of 35 kDa subunits, whereas G6PDH-2 was a dimer of 60 kDa subunits. The pIs of G6PDH-1 and G6PDH-2 were 6.4 and 5.7, respectively. Both G6PDH-1 and G6PDH-2 were inhibited by both ATP and oleic acid, but G6PDH-1 was found to be more susceptible to oleic acid than G6PDH-2. The profound inhibition of both enzymes by beta-naphthoquinone-4-sulfonic acid suggests the involvement of lysine at their active sites. Cu2+ was a potent inhibitor to G6PDH-2, but a lesser degree to G6PDH-1. Both G6PDH-1 and G6PDH-2 showed an optimum activity at pH 8.0 and 30 degrees .
Sung
Ji Youn
JY
Division of Life Sciences, College of Natural Sciences, Chungbuk National University, Cheongju 361-763, Republic of Korea.
Lee
Young Nam
YN
D000255:Adenosine Triphosphate / Q000494:pharmacology; D002384:Catalysis / Q000187:drug effects; D034301:Deinococcus / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D004591:Electrophoresis, Polyacrylamide Gel; D005954:Glucosephosphate Dehydrogenase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D008970:Molecular Weight; D019301:Oleic Acid / Q000494:pharmacology; D018384:Oxidative Stress; D013481:Superoxides / Q000494:pharmacology; D013696:Temperature
D007527:Isoenzymes; D013481:Superoxides; C039316:potassium superoxide; D019301:Oleic Acid; D000255:Adenosine Triphosphate; D005954:Glucosephosphate Dehydrogenase