Studies on the Effect of Temperature on the Activity and Stability of Cyanobacterial ADPglucose Pyrophosphorylase

D.F. GÓMEZ CASATI, J. PREISS Y A.A. IGLESIAS

ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS

Academic Press

Año: 2000 vol. 384 p. 319 - 326

0003-9861

The effect of temperature on the activity and stabilityof ADPglucose pyrophosphorylase from AnabaenaPCC 7120 was studied. Experimental optima temperatureswere found around 37–40°C or 42–45°C, dependingon the absence or the presence of allosteric effectorsin the assay medium, respectively. In the range oftemperature where the enzyme is stable, curved Arrheniusplots were obtained, indicating a transitiontemperature between 9 and 12°C. Since these resultswere observed for both the forward and reverse reaction,with two different sets of substrates and twoentirely different assay procedures, it seems unlikelythat the effect can be on any component of the systemother than the enzyme itself. Results suggest that cyanobacterialADPglucose pyrophosphorylase undergoesconformational changes at different temperatures,rendering structures with different catalytic efficiencies.The different structures of the enzyme werevisualized by emission fluorescence. ADPglucose pyrophosphorylasewas irreversibly inactivated when exposedto temperatures above 40°C. Inactivation wasdependent on temperature and followed first orderkinetics. The substrate, ATP, and the allosteric effectors,3PGA and Pi, effectively protected the enzymeagainst thermal inactivation. Protection afforded byATP was affected by MgCl2. These results suggest thatthe binding of the effectors to the enzyme resulted inconformational changes of the protein, renderingstructures more stable to temperature treatments.Similar structures could be adopted by the enzyme indifferent environments, since the higher stability wasobserved in media containing either high ionicstrength or high hydrophobicity. © 2000 Academic Press