Purification and characterisation of cathepsin L from the skeletal muscle of blue scad (Decapterus maruadsi) and comparison of its role with myofibril-bound serine proteinase in the degradation of myofibrillar proteins

The modori phenomenon during surimi production is caused by endogenous proteinases, especially cathepsin L and myofibril-bound serine proteinase (MBSP). Cathepsin L from the skeletal muscle of blue scad (Decapterus maruadsi) was purified to homogeneity by ammonium sulphate fractionation and a series of column chromatographies and revealed a single band with molecular mass of 30 kDa on SDS-PAGE. Peptide mass fingerprinting (PMF) obtained three fragments with 48 amino acid residues, which were highly identical to cathepsin L from other fish species. Its optimal pH and temperature were 5.5 and 55 degrees C, respectively. Meanwhile, MBSP was purified from the skeletal muscle of blue scad, and the roles of cathepsin L and MBSP in the degradation of myofibrillar proteins were compared. The results indicated that MBSP is more effective than cathepsin L in promoting the degradation of myofibrillar proteins, especially myosin heavy chain (MHC), suggesting that MBSP plays a more significant role. (C) 2012 Elsevier Ltd. All rights reserved.