Associated Faculty
  Internal Users

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William C. Plaxton

  Plant biochemistry and metabolic regulation

  Contact Information:  
  Professor of Biology & Associate Professor of Biochemistry
B.Sc., Ph.D., Carlton University;
C. D. Nelson Award, Canadian Society of Plant Physiologists

Tel: (613) 533-6150
Fax: (613) 533-6617
email: plaxton@biology.queensu.ca

  Lab Overview

The aim of our research is to examine the mechanisms whereby vascular plants, unicellular green algae, and cyanobacteria control and coordinate the activities of the enzyme catalyzed chemical reactions that collectively constitute metabolism. Owing to the incredible complexity and unique flexibility of plant metabolism and bioenergetics this area of research is challenging, fascinating, and rewarding. Our focus is on: (i) the purification and characterization of various key regulatory (allosteric) enzymes of plant and algal carbohydrate and phosphate metabolism, and (ii) the metabolic adaptations of plants to nutritional phosphate starvation. Systems we study include germinating and developing oilseeds, canola and tomato suspension cell cultures, and chemostat-cultured unicellular green algae and cyanobacteria. This work is providing a better understanding of how plant and algal cells "fine tune" their internal metabolic processes so as to cope with an ever-changing and stressful environment. As the tools of biotechnology become more refined, our areas of research focus will increase in importance as targets for crop improvement.

Why Should You be Interested in Learning Enzyme/Protein Biochemistry?

With many genomes sequenced and others nearing completion, the next step is the less straightforward task of analyzing gene product (protein) function and expression, as well as more thoroughly elucidating metabolism and its control. Getting a better grasp of proteins and their actions and reactions is one of the biggest challenges facing life science researchers today! As about 90% of known proteins are enzymes, most of this attention is being directed towards understanding enzyme structure-function and regulation. Nevertheless, a fairly common misconception is that the process of biotechnology and genetic engineering almost exclusively involves the manipulation of the nucleic acids, DNA & RNA. Yet, the ability to carry out protein, enzyme, & metabolic biochemistry has many direct and highly relevant applications to the biotech industry and molecular biology in general. Indeed, those who can effectively integrate protein/enzyme research with molecular biological techniques will be particularly sought after by many employers in the biotech sector. Efficient approaches for identifying proteins, for determining protein expression in different cells under various conditions, for identifying covalent modifications of proteins in response to different stimuli, and for characterizing protein interactions will be critical for understanding biological processes in the post-genome era. New methods are also being developed to map proteomes (e.g., the proteins encoded by the genome) and to discover enzymes of interest.

Lab Equipment:

Thanks to NSERC, we have acquired many of the latest tools for purifying and characterizing enzyme proteins, including the state-of-the-art Pharmacia ƒKTA FPLC system (for protein purification - the first on the Queen's campus), a Waters HPLC, a Perkin-Elmer Spectrofluorometer, as well as two PC-controlled kinetic microplate readers (that greatly facilitate enzyme activity determinations and kinetic studies). We are also making considerable use of the proteomics facility that was recently established in the Dept. of Biochemistry at Queen's. This facility will play a prominent role in ongoing research to discover novel intra- and extracellular proteins that are specifically induced by phosphate starvation of our plant suspension cell cultures.

  Selected recent publications...

Plaxton WC (2003) Principles of Metabolic Control. In: Functional Metabolism of Cells: Control, Regulation, and Adaptation (K Storey, ed). John Wiley & Sons, Inc., N.Y. (in press)

Plaxton WC (2003) Biochemical Adaptations of Phosphate Starved Plants. In: Encyclopedia of Plant & Crop Science (R Goodman, ed), Marcel Dekker, N.Y. (in press)

Blonde JD, Plaxton WC (2003) Structural and kinetic properties of high and low molecular mass phosphoenolpyruvate carboxylase isoforms from the endosperm of developing castor oil seeds. J Biol Chem 278: 11867-11873

Podestà FE, Plaxton WC (2003) Fluorescence study of ligand binding to potato tuber pyrophosphate-dependent phosphofructokinase: evidence for competitive binding between fructose-1,6-bisphosphate and fructose-2,6-bisphosphate. Arch Biochem Biophys 414: 101-107

Turner WL, Plaxton WC (2003) Purification and characterization of pyrophosphate- and ATP-dependent phosphofructokinases from banana fruit. Planta 217: 113-121

Knowles VL, Plaxton WC (2003) From genome to enzyme: Quantitative analysis of glycolytic and oxidative pentose pathway enzymes from the cyanobacterium Synechocystis PCC 6803. Plant Cell Physiol (in press)

Bozzo G, Raghothama KG, Plaxton WC (2002) Purification and characterization of two secreted purple acid phosphatase isozymes from phosphate-starved tomato cell cultures. Eur J Biochem 269: 6278-6287

Plaxton WC, Knowles VL, Smith CR (2002) Molecular and regulatory properties of leucoplast pyruvate kinase from Brassica napus (rapeseed) suspension cells. Arch Biochem Biophys 400: 54-62

Rivoal J, Smith CR, Moraes TF, Turpin DH, Plaxton WC (2002) Enzyme activity staining after native polyacrylamide gel electrophoresis using fluorescence detection. Analyt Biochem 300: 94-99

Rivoal J, Turpin DH, Plaxton WC (2002) In vitro phosphorylation of phosphoenolpyruvate carboxylase from the green alga Selenastrum minutum. Plant Cell Physiol 43: 785-792

Knowles VL, Smith CR, Smith CS, Plaxton WC (2001) Structural and regulatory properties of pyruvate kinase from the cyanobacterium Synechococcus PCC 6301. J Biol Chem 276: 20966-20972

Rivoal J, Trzos S, Gage DA, Plaxton WC, Turpin DH (2001) Two unrelated phosphoenolpyruvate carboxylase polypeptides physcically interact in the high molecular mass isoform of this enzyme in the unicellular green alga Selenastrum minutum. J Biol Chem 276: 12588-12597.

Palma DA, Blumwald E, Plaxton WC (2000) Upregulation of vacuolar H+-translocating pyrophosphatase by phosphate starvation of Brassica napus (rapeseed) suspension cell cultures. FEBS Letts 486, 155-158.

Turner WL, Plaxton WC (2000) Purification and characterization of cytosolic pyruvate kinase from banana fruit. Biochem J 352, 875-882.

Moraes T, Plaxton WC (2000) Purification and characterization of phosphoenolpyruvate carboxylase from Brassica napus (rapeseed) suspension cell cultures. Implications for phosphoenolpyruvate carboxylase regulation during phosphate starvation, and the integration of glycolysis with nitrogen assimilation. Eur J Biochem. 267, 4465-4476.

Smith CR, Knowles VL, Plaxton WC (2000) Purification and characterization of cytosolic pyruvate kinase from Brassica napus (rapeseed) suspension cell cultures. Implications for the integration of glycolysis with nitrogen assimilation. Eur J Biochem. 267, 4477-4485.

Hodgson RJ, Jia Z, Plaxton WC (1998) Effector induced conformation changes in castor seed cytosolic fructose-1,6-bisphosphatase: A kinetic and fluorometric study. Biochim Biophys Acta 1388: 285-294.

Law RD, Plaxton WC (1997) Regulatory phosphorylation of banana fruit phosphoenolpyruvate carboxylase by a copurifying phosphoenolpyruvate carboxylase kinase. Eur J Biochem 247: 642-651.

Plaxton WC (1996) The organization and regulation of plant glycolysis. Annu Rev Plant Physiol Plant Mol Biol 47: 185-214.