title: Competitive inhibition of phosphoglucose isomerase of apple leaves by sorbitol 6-phosphate.
abstract: Apple leaf cytosolic phosphoglucose isomerase (PGI, EC 5.3.1.9) was purified to an apparent homogeneity with a specific activity of 2456 units/mg protein, and chloroplastic PGI was partially purified to a specific activity of 72 units/mg protein to characterize their biochemical properties. These two isoforms showed differential responses to heat treatment; incubation at 50 degrees C for 10 min resulted in a complete loss of the chloroplastic PGI activity, whereas the cytosolic PGI only lost 50% of its activity. Apple cytosolic PGI is a dimeric enzyme with a molecular mass of 66 kDa for each monomer. The activity of both isoforms was strongly inhibited by erythrose 4-phosphate (E4P) with a K(i) of 1.2 and 3.0 microM for the cytosolic PGI and chloroplastic PGI, respectively. Sorbitol 6-phosphate (Sor6P), an intermediate in sorbitol biosynthesis, was found to be a competitive inhibitor for both cytosolic and chloroplastic PGIs with a K(i) of 61 and 40 microM, respectively. PGIs from both spinach and tomato leaves were also inhibited by Sor6P in a similar manner. The possible physiological significance of this finding is discussed.
authors.affiliation: Department of Horticulture, 134A Plant Science, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhou
authors.forename: Lailiang
authors.initials: L
authors.lastname: Cheng
mesh_terms: D002237:Carbohydrate Dehydrogenases / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D005636:Fructosephosphates / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D005956:Glucose-6-Phosphate Isomerase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D006600:Hexosephosphates / Q000494:pharmacology*; D006358:Hot Temperature; D018551:Solanum lycopersicum / Q000201:enzymology; D027845:Malus / Q000187:drug effects* / Q000201:enzymology*; D018515:Plant Leaves / Q000187:drug effects* / Q000201:enzymology*; D030821:Plants, Genetically Modified; D018724:Spinacia oleracea / Q000201:enzymology; D013403:Sugar Phosphates / Q000494:pharmacology
chemical_list: D005636:Fructosephosphates; D006600:Hexosephosphates; D013403:Sugar Phosphates; C035752:sorbitol 6-phosphate; D019298:Glucose-6-Phosphate; C026959:erythrose 4-phosphate; C027618:fructose-6-phosphate; D002237:Carbohydrate Dehydrogenases; D005956:Glucose-6-Phosphate Isomerase