Calcium Binding by Particle-Free Supernatants of Homogenates of Skeletal Muscle

A high molecular weight fraction of a soluble Marsh muscle-relaxing preparation has been shown to contain a calcium-complexing substance. By examining the nature of the competition between this fraction and chelex-100 for calcium at various total calcium concentrations it has been possible to calculate the concentration and calcium stability constant of this calcium-complexing substance. Taking into account dilutions which occur during the preparation of fractions containing this substance its concentration may be estimated at about 2.10(-4) in muscle and its calcium stability constant was found to be about 1.5.10(5)M(-1). Preliminary evidence suggests that the calcium-binding substance is a protein.