title: The futile cycling of hexose phosphates could account for the fact that hexokinase exerts a high control on glucose phosphorylation but not on glycolytic rate in transgenic potato (Solanum tuberosum) roots.
abstract: The metabolism of potato (Solanum tuberosum) roots constitutively over- and underexpressing hexokinase (HK, EC 2.7.1.1) was examined. An 11-fold variation in HK activity resulted in altered root growth, with antisense roots growing better than sense roots. Quantification of sugars, organic acids and amino acids in transgenic roots demonstrated that the manipulation of HK activity had very little effect on the intracellular pools of these metabolites. However, adenylate and free Pi levels were negatively affected by an increase in HK activity. The flux control coefficient of HK over the phosphorylation of glucose was measured for the first time in plants. Its value varied with HK level. It reached 1.71 at or below normal HK activity value and was much lower (0.32) at very high HK levels. Measurements of glycolytic flux and O(2) uptake rates demonstrated that the differences in glucose phosphorylation did not affect significantly glycolytic and respiratory metabolism. We hypothesized that these results could be explained by the existence of a futile cycle between the pools of hexose-Ps and carbohydrates. This view is supported by several lines of evidence. Firstly, activities of enzymes capable of catalyzing these reactions were detected in roots, including a hexose-P phosphatase. Secondly, metabolic tracer experiments using (14)C-glucose as precursor showed the formation of (14)C-fructose and (14)C-sucrose. We conclude that futile cycling of hexose-P could be partially responsible for the differences in energetic status in roots with high and low HK activity and possibly cause the observed alterations in growth in transgenic roots. The involvement of HK and futile cycles in the control of glucose-6P metabolism is discussed.
authors: Institut de Recherche en Biologie Végétale, Université de Montréal, Montréal, Québec, Canada.
authors: Eric
authors: E
authors: Claeyssen
authors: Sonia
authors: S
authors: Dorion
authors: Audrey
authors: A
authors: Clendenning
authors: Jiang Zhou
authors: JZ
authors: He
authors: Owen
authors: O
authors: Wally
authors: Jingkui
authors: J
authors: Chen
authors: Evgenia L
authors: EL
authors: Auslender
authors: Marie-Claude
authors: MC
authors: Moisan
authors: Mario
authors: M
authors: Jolicoeur
authors: Jean
authors: J
authors: Rivoal
mesh_terms: D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism*; D006600:Hexosephosphates / Q000378:metabolism; D010766:Phosphorylation; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000378:metabolism; D011198:Solanum tuberosum / Q000201:enzymology / Q000378:metabolism; D015219:Substrate Cycling
chemical_list: D006600:Hexosephosphates; D006593:Hexokinase; D005947:Glucose
references: Plant Physiol. 1993 Feb;101(2):339-344
references: 12231689
references: J Exp Bot. 2001 May;52(358):881-9
references: 11432905
references: Eur J Biochem. 2000 Jul;267(14):4465-76
references: 10880970
references: Proc Natl Acad Sci U S A. 1992 Jun 1;89(11):4884-7
references: 1534409
references: FEBS Lett. 1997 Nov 24;418(1-2):47-52
references: 9414093
references: Anal Biochem. 2011 Feb 1;409(1):144-9
references: 20971056
references: Am J Physiol. 1995 Apr;268(4 Pt 1):E775-88
references: 7733279
references: Eur J Biochem. 1996 Apr 1;237(1):240-6
references: 8620879
references: Nature. 1970 Aug 15;227(5259):680-5
references: 5432063
references: Biochem J. 2001 Sep 1;358(Pt 2):437-45
references: 11513743
references: Mol Cell Biochem. 1992 Sep 22;115(1):1-9
references: 1435758
references: Plant Physiol. 1993 Jan;101(1):303-312
references: 12231686
references: Curr Opin Plant Biol. 2012 Jun;15(3):282-92
references: 22541711
references: Plant Mol Biol. 1999 Nov;41(4):465-79
references: 10608657
references: Arch Biochem Biophys. 2002 Apr 1;400(1):54-62
references: 11913971
references: Plant Physiol. 1993 Feb;101(2):553-560
references: 12231709
references: Protein Expr Purif. 2006 May;47(1):329-39
references: 16376570
references: Anal Biochem. 1976 May 7;72:248-54
references: 942051
references: Plant Physiol. 2000 May;123(1):403-12
references: 10806257
references: Biochem J. 1992 Sep 1;286 ( Pt 2):313-30
references: 1530563
references: Plant Physiol. 1989 Aug;90(4):1275-8
references: 16666922
references: Biochem J. 1996 Dec 1;320 ( Pt 2):487-92
references: 8973557
references: Plant Physiol. 1999 Sep;121(1):123-34
references: 10482667
references: Arch Biochem Biophys. 1994 Aug 1;312(2):326-35
references: 8037444
references: Trends Biochem Sci. 1995 Jan;20(1):3-10
references: 7878741
references: J Biol Chem. 1986 Mar 5;261(7):3193-9
references: 3005285
references: Phytochemistry. 2007 Mar;68(6):709-31
references: 17234224
references: Plant Physiol. 1996 Jan;110(1):105-110
references: 12226174
references: Plant Physiol. 1996 May;111(1):187-194
references: 12226284
references: Am J Physiol Endocrinol Metab. 2003 Nov;285(5):E958-63
references: 12865258
references: Trends Biochem Sci. 1998 Dec;23(12):467-8
references: 9868365
references: J Biol Chem. 1992 Jul 15;267(20):13903-9
references: 1629190
references: Biotechnol Bioeng. 2005 Jan 20;89(2):138-47
references: 15584028
references: J Biol Chem. 1988 Sep 5;263(25):12278-87
references: 3137224
references: Annu Rev Plant Physiol Plant Mol Biol. 1996 Jun;47:273-298
references: 15012290
references: Plant Physiol. 1989 Jun;90(2):734-41
references: 16666836
references: Trends Plant Sci. 2010 Feb;15(2):89-97
references: 20036181
references: FEBS Lett. 1988 Jun 6;233(1):83-6
references: 2968280
references: Proc Natl Acad Sci U S A. 1997 Apr 29;94(9):4372-7
references: 9113996
references: Diabetes. 1998 Sep;47(9):1392-8
references: 9726226
references: Biochem J. 1966 Apr;99(1):102-7
references: 4290548
references: Plant J. 1998 Jul;15(1):109-18
references: 19422146
references: Annu Rev Plant Physiol Plant Mol Biol. 1996 Jun;47:185-214
references: 15012287
references: Science. 2003 Apr 11;300(5617):261-3
references: 12690178
references: J Plant Physiol. 2011 Mar 1;168(4):299-308
references: 20889232
references: Eur J Biochem. 1974 Feb 15;42(1):107-20
references: 4364392
references: Planta. 1993 Mar;189(3):329-39
references: 24178489
references: Plant J. 2004 Mar;37(5):654-67
references: 14871307
references: Plant Physiol. 2000 Sep;124(1):71-84
references: 10982423
references: J Biol Chem. 1995 Jun 2;270(22):13147-59
references: 7768910
references: Plant Cell. 1999 Jul;11(7):1253-66
references: 10402427
references: Planta. 2001 Jan;212(2):250-63
references: 11216846
references: Plant Physiol. 1994 Nov;106(3):1179-1185
references: 12232401
references: Planta. 2012 Oct;236(4):1177-90
references: 22678033
references: Plant Mol Biol. 2002 Jul;49(5):491-501
references: 12090625
references: Planta. 1993;190(4):498-10
references: 7763823
references: Trends Biochem Sci. 1998 May;23(5):162-9
references: 9612078
references: Plant Physiol. 2005 Aug;138(4):2220-32
references: 16024683
references: Plasmid. 1979 Oct;2(4):617-26
references: 231271
references: Science. 2003 Apr 11;300(5617):332-6
references: 12690200
references: Graefes Arch Clin Exp Ophthalmol. 1996 Aug;234(8):521-6
references: 8858359
references: J Exp Biol. 2003 Jun;206(Pt 12):2049-57
references: 12756287
references: J Biol Chem. 2002 Nov 15;277(46):43948-60
references: 12226084
references: Plant Physiol. 2012 May;159(1):47-51
references: 22451715
references: Arch Biochem Biophys. 1998 Jul 15;355(2):189-96
references: 9675026
references: Plant Physiol. 2001 Dec;127(4):1836-44
references: 11743127
references: J Biol Chem. 1994 Oct 14;269(41):25502-14
references: 7929251
references: Trends Biochem Sci. 2001 May;26(5):310-7
references: 11343924
references: Planta. 2002 Mar;214(5):741-50
references: 11882943
references: Biotechnol Bioeng. 1998 Jul 20;59(2):203-13
references: 10099331
references: Yeast. 1998 Feb;14(3):255-69
references: 9580251