The calpains calcium-activated neutral proteases are nonlysosomal intracellular cysteine proteases The mammalian calpains include ubiquitous stomach-specific and muscle-specific proteins The ubiquitous enzymes consist of heterodimers with distinct large catalytic subunits associated with a common small regulatory subunit This gene encodes the large subunit of the ubiquitous enzyme calpain 1 Several transcript variants encoding two different isoforms have been found for this gene