Identification of Both Calpains I and II in Nucleated Chicken Erythrocytes

Abstract

Chicken erythrocytes were found to contain two species of calpains which differ in elution profile from DEAE-cellulose and in Ca²⁺ requirement. After partial purification, one of them was half-maximally activated by 10 μM Ca²⁺ and the other by 180 μM Ca²⁺ The lowand high-Ca²⁺-requiring proteases cross-reacted only with the respective monospecific antibodies for mammalian calpain 1 and calpain II, respectively. Approximately 5 times more calpain I than calpain II is present in chicken erythrocytes. By immunoelectropho-retic blot analysis, both calpains I and II from chicken erythrocytes were proved to be heterodimers composed of 76 and 28 kDa, and 80 and 28 kDa subunits, respectively. Our present finding that the heavy subunit of calpain I is smaller than that of calpain II is noteworthy, since the opposite is known to be true of various mammalian calpains. An immunological study has revealed that the calpain I newly found in chicken erythrocytes is not derived from calpain II. Thus, the co-existence of calpains I and II in one animal species also holds in chickens, contrary to the previously advocated notion that chickens have only one type of calpain.