Effect of 6-phosphogluconate on phosphoglucose isomerase in rat brain in vitro and in vivo.
The activity of phosphoglucose isomerase, its kinetic properties, and the effect of 6-phosphogluconate on its activity in the forward (glucose 6-phosphate----fructose 6-phosphate) and the reverse (fructose 6-phosphate----glucose 6-phosphate) reactions were determined in adult rat brain in vitro. The activity of phosphoglucose isomerase (in nmol/min/mg of whole brain protein) was 1,865 +/- 20 in the forward reaction and 1,756 +/- 32 in the reverse reaction at pH 7.5. It was 1,992 +/- 28 and 2,620 +/- 46, respectively, at pH 8.5. The apparent Km and Vmax of phosphoglucose isomerase were 0.593 +/- 0.031 mM and 2,291 +/- 61 nmol/min/mg of protein, respectively, for glucose 6-phosphate and 0.095 +/- 0.013 mM and 2,035 +/- 98 nmol/min/mg of protein, respectively, for fructose 6-phosphate. The activity of phosphoglucose isomerase was inhibited intensely and competitively by 6-phosphogluconate, with an apparent Ki of 0.048 +/- 0.005 mM for glucose 6-phosphate and 0.042 +/- 0.004 mM for fructose 6-phosphate as the substrate. With glucose 6-phosphate as the substrate, at concentrations from 0.05 to 0.5 mM, the activity of the enzyme was inhibited completely in the presence of 0.5-2.0 mM 6-phosphogluconate. With 0.05-0.2 mM fructose 6-phosphate as the substrate, it was inhibited greater than or equal to 85% at the same concentrations of the inhibitor. No significant changes were observed in the values of Km, Vmax, and Ki for phosphoglucose isomerase in the brain of 6-aminonicotinamide-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Gaitonde
M K
MK
Department of Biochemistry, St. George's Hospital Medical School, London, England.
Murray
E
E
Cunningham
V J
VJ
D015120:6-Aminonicotinamide / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects / Q000201:enzymology*; D003847:Deoxyglucose / Q000494:pharmacology; D005636:Fructosephosphates / Q000378:metabolism; D005942:Gluconates / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate; D005956:Glucose-6-Phosphate Isomerase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005958:Glucosephosphates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013053:Spectrophotometry
D000596:Amino Acids; D005636:Fructosephosphates; D005942:Gluconates; D005958:Glucosephosphates; D015120:6-Aminonicotinamide; D019298:Glucose-6-Phosphate; C027618:fructose-6-phosphate; D003847:Deoxyglucose; D005956:Glucose-6-Phosphate Isomerase; D005947:Glucose; C008884:6-phosphogluconic acid