Susceptibility of opioid peptides and myofibrillar proteins to carp cathepsin

The ability of carp cathepsin L to degrade opioid peptides and separate myofibrillar proteins was examined. The enzyme differentially released fragments from leucine-enkephalin, alpha-neoendorphin, and dynorphin, in which the common cleavage site of the enzyme was determined to be a Gly2-Gly3 bond. A Leu5-Arg6 bond in alpha-neoendorphin and dynorphin was also commonly cleaved by the enzyme. At a protein ratio of the enzyme to myofibrillar protein of 1:500, the preferences of the enzyme appeared to be myosin > tropomyosin > troponins T, I, and C > actin > alpha-actinin. Myosin heavy chain was completely degraded into some fragments by the enzyme within 30 min, and all of them underwent further degradation during subsequent incubation. Although troponins and tropomyosin were also completely degraded by the enzyme within 24 h, a small amount of actin and a large amount of alpha-actinin remained undegraded.