Creatine Kinase Equilibration and ΔGATP over an Extended Range of Physiological Conditions: Implications for Cellular Energetics, Signaling, and Muscle Performance

Abstract

In this report, we establish a straightforward method for estimating the equilibrium constant for the creatine kinase reaction (CK Keq″) over wide but physiologically and experimentally relevant ranges of pH, Mg2+ and temperature. Our empirical formula for CK Keq″ is based on experimental measurements. It can be used to estimate [ADP] when [ADP] is below the resolution of experimental measurements, a typical situation because [ADP] is on the order of micromolar concentrations in living cells and may be much lower in many in vitro experiments. Accurate prediction of [ADP] is essential for in vivo studies of cellular energetics and metabolism and for in vitro studies of ATP-dependent enzyme function under near-physiological conditions. With [ADP], we were able to obtain improved estimates of ΔGATP, necessitating the reinvestigation of previously reported ADP- and ΔGATP-dependent processes. Application to actomyosin force generation in muscle provides support for the hypothesis that, when [Pi] varies and pH is not altered, the maximum Ca2+-activated isometric force depends on ΔGATP in both living and permeabilized muscle preparations. Further analysis of the pH studies introduces a novel hypothesis around the role of submicromolar ADP in force generation.

Ryanodine receptor‐associated myopathies: What's myosin got to do with it?

“…These secondary effects on myosin in turn alter contractility in skeletal muscles and contribute to RYR1 pathology. The signal(s) that triggers changes in PTMs could be cytoplasmic Ca 2+ (Figure 1), 24,25 but could also be associated with altered ATP hydrolysis and cellular energetics, 26 and could additionally involve changes in force with corresponding effects on thick filament structure. 22 The study by Sonne et al provides a significant roadmap for wider exploration of genetic diseases beyond the molecule coded for by the affected gene.…”