This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Doehlert, D. C. Search for Related Content PubMed PubMed Citation Articles by Doehlert, D. C. Agricola Articles by Doehlert, D. C.

Metabolism and Enzymology

Separation and Characterization of Four Hexose Kinases from Developing Maize Kernels

Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604, Seed Biosynthesis Research Unit, Northern Regional Research Center, 1815 North University Street, Peoria, Illinois 61604

Four forms of hexose kinase activity from developing maize (Zea mays L.) kernels have been separated by ammonium sulfate precipitation, gel filtration chromatography, blue-agarose chromatography, and ion exchange chromatography. Two of these hexose kinases utilized D-glucose most effectively and are classified as glucokinases (EC 2.7.1.2). The other two hexose kinases utilized only D-fructose and are classified as fructokinases (EC 2.7.1.4). All hexose kinases analyzed had broad pH optima between 7.5 and 9.5 with optimal activity at pH 8.5. The two glucokinases differed in substrate affinities. One form had low K_m values [K_m(glucose) = 117 micromolar, K_m(ATP) = 66 micromolar] whereas the other form had much higher K_m values [K_m(glucose) = 750 micromolar, K_m(ATP) = 182 micromolar]. Both fructokinases had similar substrate saturation responses. The K_m(fructose) was about 130 micromolar and the K_m(ATP) was about 700 micromolar. Both exhibited uncompetitive substrate inhibition by fructose [K_i(fructose) = 1.40 to 2.00 millimolar]. ADP inhibited all four hexose kinase activities, whereas sugar phosphates had little effect on their activities. The data suggest that substrate concentrations are an important factor controlling hexose kinase activity in situ.

This article has been cited by other articles:

				R. Balasubramanian, A. Karve, M. Kandasamy, R. B. Meagher, and B. d. Moore A Role for F-Actin in Hexokinase-Mediated Glucose Signaling Plant Physiology, December 1, 2007; 145(4): 1423 - 1434. [Abstract] [Full Text] [PDF]

				U. Roessner-Tunali, B. Hegemann, A. Lytovchenko, F. Carrari, C. Bruedigam, D. Granot, and A. R. Fernie Metabolic Profiling of Transgenic Tomato Plants Overexpressing Hexokinase Reveals That the Influence of Hexose Phosphorylation Diminishes during Fruit Development Plant Physiology, September 1, 2003; 133(1): 84 - 99. [Abstract] [Full Text] [PDF]

				J. Veramendi, U. Roessner, A. Renz, L. Willmitzer, and R. N. Trethewey Antisense Repression of Hexokinase 1 Leads to an Overaccumulation of Starch in Leaves of Transgenic Potato Plants But Not to Significant Changes in Tuber Carbohydrate Metabolism Plant Physiology, September 1, 1999; 121(1): 123 - 134. [Abstract] [Full Text]

				T. C. Fox, B. J. Green, R. A. Kennedy, and M. E. Rumpho Changes in Hexokinase Activity in Echinochloa phyllopogon and Echinochloa crus-pavonis in Response to Abiotic Stress Plant Physiology, December 1, 1998; 118(4): 1403 - 1409. [Abstract] [Full Text]

				Y. Kanayama, D. Granot, N. Dai, M. Petreikov, A. Schaffer, A. Powell, and A. B. Bennett Tomato Fructokinases Exhibit Differential Expression and Substrate Regulation Plant Physiology, May 1, 1998; 117(1): 85 - 90. [Abstract] [Full Text]