Limited autolysis reduces the Ca2+ requirement of a smooth muscle Ca2+-activated protease.

摘要: Chicken gizzard smooth muscle contains large amounts of Ca2+-activated protease activity. Approximately 15 mg purified enzyme can be obtained from 1 kg fresh muscle. The consists two subunits (Mr = 80,000 and 30,000) present in a 1:1 molar ratio. In the presence CaCl2, 80,000/30,000-dalton heterodimer (form I) is rapidly converted by limited autolysis to 76,000/18,000-dalton species II). Both 80,000- 30,000-dalton are degraded simultaneously. Moreover, Ca2+ dependence for (K0.5 300 microM) identical both subunits. Neither time course nor autolytic conversion reaction altered 10- 20-fold excesses substrate. Limited markedly reduces requirement substrate degradation. Using N-[ethyl-2-3H]maleimide-labeled 27,000-dalton cardiac myosin light chains as substrate, form I was found quite high 150 microM). Under similar conditions, II 30-fold lower 5 did not alter specific activity enzyme. Our results demonstrate that an abundant amount protease. this may play important regulatory role converting native fully active at physiological levels intracellular calcium ion.