The proteolytic activity of uPA is increased in regenerating muscle after injury.

Forty micrograms of proteins from muscle extracts of noninjured (0 days AI) and injured skeletal muscle (2, 4, and 7 days AI). were analyzed after SDS-PAGE by PA zymography. Two nanograms of purified human uPA (55 kd) were utilized as a control for activity (C). The 45-kd approximate molecular mass species corresponds to murine uPA and was calculated according to standard molecular mass markers electrophoresed in an adjacent lane and stained with Coomassie blue. The photographs were taken after overnight incubation at 4°C and 4 hours at 37°C.