PROTEOLYTIC ACTIVITY OF ISOLATED LAMB CALPAINS ON MYOFIBRILS UNDER THE CONDITIONS OF PH, CA2+ CONCENTRATION AND TEMPERATURE EXISTING IN POSTMORTEM MUSCLE

The two calcium-activated neutral proteinases (calpains I and II) and their specific inhibitor were isolated by ion exchange chromatography in DEAE-Sephacel from lamb skeletal muscle (longissimus dorsi). Their proteolytic activities were then determined using myofibrils as substrate. The Ca2+ requirements were different for each form of the enzyme: calpain I needed only 50-mu-mol Ca2+ for half-maximal activity, while the other isoenzyme, calpain II, needed 1000-mu-mol Ca2+ for reaching 50% of its maximum activity. Both calpains showed a relevant activity in the pH range 5.5-6.5 (over 40% of maximum activity found at pH 7.5). With regard to the effect of temperature, both isoenzymes retained about 25% of their activity at 25-degrees-C with a temperature reduction down to 4-degrees-C. It is concluded that calpain I is an active protease under conditions similar to that prevalent in lamb meat during postmortem storage.