T. Yoshizawa et al., CALPAIN DISSOCIATES INTO SUBUNITS IN THE PRESENCE IONS, Biochemical and biophysical research communications, 208(1), 1995, pp. 376-383
Calpain is a calcium dependent cysteine protease consisting of a catal
ytic 80K subunit and a regulatory 30K subunit. It has therefore been b
elieved that calpain functions as a dimer. Here we have found that cal
pain dissociates into subunits in the presence of the Ca2+ required fo
r the expression of activity and that the dissociated 80K subunit is e
nzymatically fully active. Moreover, the 80K subunit shows a calcium s
ensitivity identical to the activated form of calpain but not to the o
riginal control calpain. The results suggest that the activation of ca
lpain corresponds to the dissociation into subunits in the presence of
Ca2+ and that calpain functions as a monomer of the 80K subunit in vi
vo. (C) 1995 Academic Press, Inc.