La calpaine II du muscle squelettique de lapin. Régulation de l'activité enzymatique : influence de la présence de phospholipides membranaires sur l'autolyse enzymatique en présence ou non de substrat

: A calcium activated neutral proteinase (calpain II) was prepared on a large scale at a high degree of purity from rabbit skeletal muscle using an original purification procedure. "In vitro" highly purified Calpain II was optimally activated by 2 mM Ca2+ and had two subunits with a molecular weight of 80 kDa and 28 kDa. The influence of membrane acid phospholipids (phosphatidyl inositol PI, phosphatidyl serine PS) and neutral phospholipids (phosphatidyl choline) on calcium enzymatic autolysis in the presence or not of substrate was electrophoretically studied. In the absence of a substrate no degradation of the catalytic subunit (80 kDa) was observed: phosphatidyl inositol and phosphatidyl serine stimulated drastically the 28 kDa subunit degradation with a release of a common 18 kDa product. In the presence of substrate (beta-globin) the 28 kDa subunit was more protected against calcium autolysis. On the other hand, phosphatidyl serine seemed to induce simultaneously 80 and 28 kDa degradations: the released breakdown products were different from those obtained with phosphatidyl inositol and phosphatidyl choline. In presence or absence of substrate, phosphatidyl choline did not affect significantly the calpain II calcium autolysis. Further studies on calpain II-membrane binding as well as its influence on calpain - activity are in progress.