Loss of immunological and biological activity of insulin with a human muscle extract

The isolation of a human muscle extract that degrades insulin to products incapable of any immunological or biological activity is reported. The extract Km value for human insulin is 0.79, and 1.43 for porcine proinsulin. It does not degrade Human Growth Hormone at the concentrations tested, it is inactivated by N-ethyl-maleimide, Trasylol, and heat, and it does not require glutathione for its action. Human muscle, therefore can contain an enzyme similar to "insulin-specific-protease" present in rat muscle.