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 1.5·10⁵ M ^-1. Preliminary evidence suggests that the calcium-binding substance is a protein.