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A1 8 Biochemical Society Transactions (1999) 27 F12 Checks and Balances in the Lipid PathwaydNetwork F14 Forging the Link, International Networking Ian D G Battle, ACTIN Director Pira House, Randalls Road, Leatherhead KT22 7RU Slabas. T. University of Durham, Department of Biology, South Road, Durham, DH13LE G1 F13 Turnover and Sequestration of Plant Secondary Products Robert Edwards, Department of Biological Sciences, University of Durham, Durham DHl 3LE. Although there has been considerable progress in understanding how plant secondary products are synthesised,surprisingly little is known concerning how they are turned over and degraded. As the final concentrations of secondary products are determined by a combination of synthesis and turnover, it is important to understand how these metabolites are degraded if we are to successfully engineer secondary metabolism in plants. Many plant secondary products are conjugated with sugars and stored in the vacuole. But this is not an end-point of metabolism and these conjugates undergo rapid cycling and can be re-released or further degradaded. Using our studies on inducible isoflavonoid phytoalexin metabolism in legumes as an example, the pathways responsible for the conjugation, storage and turnover of phenolic secondary metabolites will be discussed. In alfalfa (Medicago sufivu)the isoflavonoid phytoalexin medicarpin is degraded by a combination of oxidative enzymes and sugar conjugation. Evidence will be presented that the enzymes responsible for the conjugation of isoflavonoids are highly specific and their expression regulated by exposure to their aglycone substrates. After conjugation,the sugar moiety of isoflavonoid conjugates becomes 6"-O-malonylatedand this modification appears to target secondary products for vacuolar deposition. The mechanisms whereby conjugates of secondary metabolites are taken up into the vacuole is not well understood, but drawing parallels with the metabolism of xenobiotics, probably involves active transport and ATP-binding cassette transporter proteins, which may act in conjunction with glutathione transferases. Finally these conjugates are readily turned over by re-release into the cytoplasm by specific hydrolases and can be recycled back into bioactive isoflavonoids for use in defence against fungal infection. Live Control of the Living Cell Wally C. van Heeswijk, Barbara M. Bakker, Bas Teusink, Boris N. Kholodenko, Oscar J.G. Somsen, Jacky L. Snoep and Hans V. Westerhoff Molecular Cell Physiology & Mathematical Biochemistry, BioCentrum Amsterdam, Biology, De Boelelaan 1087 NL- 1081 HV Amsterdam, European Union Many studies of metabolic control address the question which molecular processes determine a flux. Metabolic Control Analysis has rephrased this question as the extent to which activation of any such process activates that flux. We shall discuss how the control of the glycolytic flux in T. brucei, a mammalian parasite involved in sleeping disease, is distributed over glucose transport and a number of glycolytic enzymes. The distribution of control is itself not constant but a strong hnction of extracellular glucose concentration and of the activity of the glucose carrier. The phenomenon of a strong dependence of metabolic control on the activities of certain cellular components suggests that living cells may be able to adjust their metabolic control to their needs: Metabolic control itself may be a live property of living cells, through differential activation of the cellular control hierarchies. The variety of glucose transporters in S. cerevisiae might serve this purpose. We shall discuss an example of such live control, i.e., that of ammonia assimilation in E. coli by the pivotal protein PI1 and its homologue GlnK. Depending on the growth history of the cells, GlnK attenuates the control exerted by PII. Molecular intelligence may be the result.