ADJUSTMENT OF K' FOR THE CREATINE-KINASE, ADENYLATE KINASE AND ATP HYDROLYSIS EQUILIBRIA TO VARYING TEMPERATURE AND IONIC-STRENGTH

Comparative physiologists and biochemists working with tissues at vary ing temperatures and ionic strength are required to adjust apparent eq uilibrium constants (K') of biochemical reactions to the experimental conditions prior to calculating cytosolic bioenergetic parameters (tra nsformed Gibbs free energy of formation, Delta(f)G'(ATP); cytosolic ph osphorylation ratio, [ATP]/[ADP][P-i]; [phosphocreatine]:[orthophospha te] ratio [PCr]/[P-i]) and kinetic parameters (free [ADP], [P-i] and [ AMP]). The present study shows how to adjust both K' and the equilibri um constants of reference reactions (K-ref) of creatine kinase (ATP: c reatine N-phosphotransferase; EC 2.7.3.2), adenylate kinase (ATP:AMP p hosphotransferase; EC 2.7.4.3) and adenosinetriphosphatase (ATP phosph ohydrolase; EC 3.6.1.3) to temperature and ionic strength. This inform ation, together with our previous study showing how to adjust equilibr ia to varying pH and pMg, is vital for the quantification of organ and tissue bioenergetics of ectotherms and endotherms under physiological conditions.