Concurrent identification of calpains I and II from chicken skeletal muscle

A single anion-exchange column resolved two peaks of calcium-activated neutral protease activity, corresponding to the two calpain forms chicken skeletal muscle. Multiple columns have previously been needed to resolve the two isoforms from avian tissue. Calcium requirement assays confirmed one form to require approximately 100 microM Ca2+ for half-maximal activity, while the other required approximately 500 microM Ca2+. Electrophoresis revealed that the enzymes were not purified to homogeneity.