Comparison of low- and high-calcium-requiring forms of the calcium-activated protease with their autocatalytic breakdown products.

The effect of controlled autocatalytic degradation on the subunit molecular weight, subunit composition and calcium sensitivity of the low-calcium-requiring and the high-calcium-requiring forms of the calcium-activated muscle protease was examined. Purified low- and high-calcium-requiring proteases coelectrophorese on SDS-polyacrylamide gels. Controlled autocatalysis of either form of the protease results in extensive degradation of their respective 30 kDa subunits and partial degradation of their 80 kDa subunits. In this electrophoresis system the electrophoretic banding pattern of the low-calcium-requiring protease is clearly different from that of the autocatalytically degraded high-calcium-requiring protease. Similar results were obtained using a nondenaturing polyacrylamide gel system. Both the high- and low-calcium-requiring proteases were made more sensitive to calcium by autocatalytic degradation. However, the results of this study strongly indicate that autocatalytic degradation does not result in conversion of high-calcium-requiring protease to the low-calcium-requiring protease as has been recently hypothesized (Suzuki et al. (1981) J. Biochem. 90, 275-278).