Protection and Reactivation of Cardioglobulin-A by High Energy Phosphate Compounds

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Abstract
The biological activity of cardioglobulin-A can be destroyed enzymatically by a short equilibration with homogenates prepared from a wide variety of tissues. Blood plasma alone also contains a cardioglobulin-A inactivating system which is stimulated by the removal or dilution of an unidentified small molecule normally present in the plasma. Inactivation of cardioglobulin-A can be prevented by the addition of certain high energy phosphate compounds, notably ATP, ADP or CP. Furthermore, the biological activity of inactivated cardioglobulin-A can frequently be restored by addition of CP. When the whole cardioglobulin system acts on the frog heart, cardioglobulin-A activity is gradually depleted. This is associated with a loss of protein-bound phosphorus from a component of the mixture. Activity can be restored by addition of CP. It has been proposed that the action of the cardioglobulin system involves the release of bound cardioglobulin-C calcium. A possible role of cardioglobulin-A may be to provide, through a ∼ P linkage, the energy for the release of this calcium.