Alkali Metal Ions Protect Mitochondrial Rhodanese against Thermal Inactivation

Incubation of bovine liver mitochondrial rhodanese in dilute, reducing solutions at temperatures ranging between 30 and 45°C conduced to a rapid loss of enzymatic activity. This inactivation was substantially reduced in the presence of millimolar concentrations of alkali metal ions, divalent cations (including Mg2+, Ca2+, and Ba2+) were ineffective. The extent of protection afforded by monovalent cations was highly dependent on their ionic radii, with K+and Na+ions being the most effective protective agents. The protection afforded by a number of anions, including thiosulfate, could be totally ascribed to the presence of the accompanying monovalent cation. The overall results indicate that K+and Na+, at concentrations and temperatures within the physiological range, substantially contribute to the stabilization of the functional structure of rhodanese.