Can a Chemolithotrophic Organism Synthesize Glycogen as a Carbon Energy Storage

M. MACHTEY; M. KUHN; M. ALEANZI; M.A. BALLICORA; A.A. IGLESIAS

San Miguel de Tucumán, Argentina

Congreso; XLV Reunión Anual de SAIB; 2009

SAIB

EN-P09.CAN A CHEMOL I THOTROF IC ORGANI SMSYNTHESIZE GLYCOGEN AS A CARBON-ENERGYSTORAGE?Machtey M1; Kuhn M2; Aleanzi MC1; Ballicora M2; Iglesias AA11Inst. Agrobiotecnología Litoral (UNL-CONICET), Santa Fe.2Dept. Chemistry, Loyola Univ. Chicago, USA. E-mail:mmachtey@fbcb.unl.edu.arGlycogen and starch serve as important energy and carbon storagecompounds for nearly all living organisms. In bacteria and plants,ADP-glucose pyrophosphorylase (ADPGlc PPase, the product ofthe glgC gene) catalyzes the rate-limiting step of the glucanbiosynthesis pathway. The regulation of this enzyme is mediated byvarious metabolites serving as allosteric activators and inhibitiorsaccording with the carbon utilization pathways. We co-expressedin Escherichia coli cells a putative glgC gene from dechemolithotrofic organism Nitrosomonas europaea using theGroEL-GroES chaperone system. This resulted in a solube andactive enzyme which was purified following ammonium sulphateprecipitation, DEAE-Sepharose and Phenyl-Sepharosechromatographies. The purified enzyme was kineticallycharacterized fitting the experimental data to the Hill equation. S 0.5for Glc-1P, ATP and Mg2+ were calculated in 0.1 mM, 0.64 mM and13 mM, respectively. The enzyme was activated 10-fold bypyruvate while phosphoenolpyruvate only activated 2-fold. TheAMP inhibited the enzyme and this effect is more notable inpresence of the pyruvate activator. This behaviour shows allostericregulation of N. europaea ADPGlc PPase, making it interesting forstructure/function relationships studies. Results support theoccurrence of glycogen metabolism in chemolithotrophes at leastfor carbon storage functions.