Mast cell origin of ‘myofibrillar protease’ of rat skeletal and heart muscle

Autolysis of a washed heavy particle fraction from rat gastrocnemius muscle was largely prevented when the animals were injected with Compound ⁴⁸/80 to degranulate mast cells. The ‘myofibrillar protease’ activity appears to be due therefore to the proteolytic enzyme from mast cells. Alkaline proteinase activity (casein substrate) in rat heart preparations was also largely depleted by Compound ⁴⁸/80. Autolytic activity was similarly affected in the heavy particle fraction but much less so in the homogenate.