N. Sargianos et al., PROTEOLYTIC DEGRADATION OF ISOLATED MYOFIBRILS AND MYOFIBRILLAR PROTEINS BY M-CALPAIN FROM THE SKELETAL-MUSCLE OF THE AMPHIBIAN RANA-RIDIBUNDA, The Journal of experimental zoology, 276(1), 1996, pp. 30-42
The effects of m-calpain isolated from the skeletal muscle of Rana rid
ibunda on the myofibril and myofibrillar proteins were examined. The r
esults of this study clearly showed that treatment of myofibrils with
calpain in the presence of 2 mM Ca2+ results in the complete disappear
ance of Z-lines within 5 min, whereas prolonged incubation results in
the appearance of single sarcomeres or groups of 2-5 sarcomeres. From
the other divalent cations examined only Sr2+ at high concentration in
duces the Z-line removal by calpain. Presence of Mn2+ or Ba2+ reduces
the Ca2+ requirement of calpain to the Z-line removal. Protease inhibi
tors such as endogenous calpastatin, E-64, and leupeptin completely in
hibit the Z-line removal by calpain, whereas PMSF and trypsin inhibito
r do not inhibit the proteolytic activity of calpain. Studies on the p
roteolytic degradation of various myofibrillar proteins isolated from
the skeletal muscle of Rana ridibunda showed that myosin and G-actin c
ould represent ''good'' substrates of calpain, whereas F-actin and tro
pomyosin are not degraded by this protease. Our results also showed th
at the optimum conditions of calpain action and function on the myofib
rillar protein degradation are quite similar to those described for bo
th its maximal caseinolytic activity (Sargianos et al. [1994] J. Exp.
Zool., 269:95-105) and autolytic modification (Sargianos et al. [1995]
J. Exp. Zool., 271:82-94). (C) 1996 Wiley-Liss, Inc.