Hydrogen ion buffers and enzymatic activity: Myosin B adenosinetriphosphatase

Abstract

The production of hydrogen ions during the hydrolysis of ATP by myosin B and the consequent fall in pH can produce alterations in enzymatic activity directly, or by influencing Ca ion concentrations controlled by metal-chelate systems. Adequate hydrogenion buffer systems can limit pH changes to acceptable levels. However, several commonly used hydrogen ion buffers have been reported to have specific effects on contractile protein responses, and all buffers can indirectly change activity through their contributions to the ionic strength. In this study, ten potentially useful buffers suitable for pH control between pH 5 and 9 were evaluated for their effects on myosin B ATPase activity. In contrast to previous reports, all were found to have no effect on this system if both the buffering value ([Delta]H+/[Delta]pH) and the ionic strength were maintained constant. Simple methods are presented for determining the total and ionized concentrations of any buffer required to meet designated criteria for pH control at any operating pH.