Calcium-ion-activated neutral proteinase of muscle is found in other tissues

Purification and characterization of m-calpain from the skeletal muscle of the amphibian Rana ridibunda

Calpain was purified to apparent homogeneity from the skeletal muscle of the amphibian Rana ridibunda. It is composed of two subunits of 78 and 28 kDa, respectively. The enzyme exhibits kinetic properties similar to those of mammalian and avian skeletal muscle m-calpains. Ca2+ requirements for half and maximum activities are 400 microM and 1.5 mM, respectively. It is strongly inhibited by thiol protease inhibitors such as leupeptin, E-64, and antipain and by alkylating thiol group agents such as iodoacetic acid (IAA), iodoacetamide (IAM), and N-ethylmaleimide (NEM). Its activity is enhanced by reduced thiols such as dithiothreitol (DTT), cysteine, and 2-mercaptoethanol. The enzyme is stable in the absence of Ca2+ at 55 degrees C, it displays maximum activity at 25 degrees C, and it shows a broad pH optimum between 6.5 and 7.8. In the absence of Ca2+, various divalent cations such as Sr2+, Mn2+, and Ba2+ strongly activate, while other divalent cations such as Ni2+, Co2+, Cd2+, Zn2+, and Cu2+ have no effect on its activity. In the presence of Ca2+, the cations Sr2+, Mn2+, and Ba2+ show a synergistic effect, while the cations of the other group strongly inhibit the calpain activity. The above data demonstrate that calpain from the skeletal muscle of the amphibian Rana ridibunda is a neutral, Ca(2+)-activated thiol protease and that it belongs to the class of m-calpains.

Ca2+-activated proteinase in the rat. Quantification by immunoassay in the uterus during pregnancy and involution, and in other tissues

Rat uteri were taken at various stages of pregnancy and involution post partum, and several other tissues were taken from pregnant and non-pregnant animals. Portions of each tissue were homogenized in the presence of proteinase inhibitors, and the amounts of the high-Ca2+-requiring Ca2+-activated proteinase in the supernatants were measured by a two-site immunoradiometric assay using 125I-immunoglobulin G. The proteinase was shown, by protein blotting, to be immunologically identical in all tissues. The amounts in the various tissues, expressed in units of proteinase activity/g wet wt., were: lung, 95; kidney and small intestine, 42; liver, 20; brain, heart and skeletal muscle, 13. Uterine wet weight increased at the end of pregnancy by about 8-fold, but the amounts of proteinase per uterus increased by about 22-fold; alternatively, expressed in units of proteinase activity/g wet wt., the mean uterine values were: non-pregnant, 28.6; term-pregnant, 77.0. As the wet weight of the uterus fell rapidly during involution, the amounts of proteinase activity remained relatively high. The data suggest that the Ca2+-activated proteinase may have some role in tissue resorption during uterine involution, but the high proteinase activity present before parturition must be regulated in ways which are not yet clear.

Isolation of two ATPase inhibitor proteins from mitochondria of rat skeletal muscle

An ATPase inhibitor protein was isolated from mitochondria of rat skeletal muscle by alkaline extraction and then was purified. It differed in definitive ways from the ATPase inhibitor protein isolated previously by Ca2+-stripping of submitochondrial particles of rat skeletal muscle. The two ATPase inhibitor proteins were shown to be present together in intact mitochondria.