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 Web of Science 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 Web of Science (78) Citing Articles via Google Scholar Google Scholar Articles by Xu, D.-P. Articles by Black, C. C. Search for Related Content PubMed PubMed Citation Articles by Xu, D.-P. Articles by Black, C. C. Agricola Articles by Xu, D.-P. Articles by Black, C. C.

Metabolism and Enzymology

Characterization of Sucrolysis via the Uridine Diphosphate and Pyrophosphate-Dependent Sucrose Synthase Pathway ¹

Department of Biochemistry of the School of Chemical Sciences, University of Georgia, Athens, Georgia 30602, Institute for Mycorrhizal Research and Development, University of Georgia, Athens, Georgia 30602

The breakdown of sucrose to feed both hexoses into glycolytic carbon flow can occur by the sucrose synthase pathway. This uridine diphosphate (UDP) and pyrophosphate (PPi)-dependent pathway was biochemically characterized using soluble extracts from several plants. The sucrolysis process required the simultaneous presence of sucrose, UDP, and PPi with their respective K_m values being about 40 millimolar, 23 micromolar, and 29 micromolar. UDP was the only active nucleotide diphosphate. Slightly alkaline pH optima were observed for sucrose breakdown either to glucose 1-phosphate or to triose phosphate. Sucrolysis incrased with increasing temperature to near 50°C and then a sharp drop occurred between 55 and 60°C. The breakdown of sucrose to triose-P was activated by fructose 2,6-P₂ which had a K_m value near 0.2 micromolar. The cytoplasmic phosphofructokinase and fructokinase in plants were fairly nonselective for nucleotide triphosphates (NTP) but glucokinase definitely favored ATP. A predicted stoichiometric relationship of unity for UDP and PPi was measured when one also measured competing UDPase and pyrophosphatase activity. The cycling of uridylates, UDP to UTP to UDP, was demonstrated both with phosphofructokinase and with fructokinase. Enzyme activity measurements indicated that the sucrose synthase pathway has a major role in plant sucrose sink tissues. In the cytoplasmic sucrose synthase breakdown pathway, a role for the PPi-phosphofructokinase was to produce PPi while a role for the NTP-phosphofructokinase and for the fructokinase was to produce UDP.

This article has been cited by other articles:

				E. Grafahrend-Belau, F. Schreiber, D. Koschutzki, and B. H. Junker Flux Balance Analysis of Barley Seeds: A Computational Approach to Study Systemic Properties of Central Metabolism Plant Physiology, January 1, 2009; 149(1): 585 - 598. [Abstract] [Full Text] [PDF]

				L. I. Sergeeva, J. J. B. Keurentjes, L. Bentsink, J. Vonk, L. H. W. van der Plas, M. Koornneef, and D. Vreugdenhil Vacuolar invertase regulates elongation of Arabidopsis thaliana roots as revealed by QTL and mutant analysis PNAS, February 21, 2006; 103(8): 2994 - 2999. [Abstract] [Full Text] [PDF]

				M. J. Emes, C. G. Bowsher, C. Hedley, M. M. Burrell, E. S. F. Scrase-Field, and I. J. Tetlow Starch synthesis and carbon partitioning in developing endosperm J. Exp. Bot., January 3, 2003; 54(382): 569 - 575. [Abstract] [Full Text] [PDF]

				Y. Zeng, Y. Wu, W. T. Avigne, and K. E. Koch Rapid Repression of Maize Invertases by Low Oxygen. Invertase/Sucrose Synthase Balance, Sugar Signaling Potential, and Seedling Survival Plant Physiology, October 1, 1999; 121(2): 599 - 608. [Abstract] [Full Text]

				T. Nakai, N. Tonouchi, T. Konishi, Y. Kojima, T. Tsuchida, F. Yoshinaga, F. Sakai, and T. Hayashi Enhancement of cellulose production by expression of sucrose synthase in Acetobacter xylinum PNAS, January 5, 1999; 96(1): 14 - 18. [Abstract] [Full Text] [PDF]