PURIFICATION AND PROPERTIES OF A CALPAIN II-LIKE PROTEINASE FROM OCTOPUS-VULGARIS ARM MUSCLE

A Ca2+-dependent proteinase was purified to homogeneity from the arm m uscle of the marine invertebrate Octopus vulgaris. The enzyme has a na tive molecular weight of similar to 520 kDa and consists of a 65-kDa p rotein when separated by SDS-polyacrylamide gel electrophoresis. The C a2+ requirements for its half maximal and maximal activities are 1.5 a nd 7 mM, respectively. It is strongly inhibited by thiol protease inhi bitors such as leupeptin, E-64 and antipain and by alkylating thiol gr oup agents such as iodoacetic acid and iodoacetamide. The enzyme is st able in the absence of Ca2+ at 42 degrees C, displays maximal activity at 30 degrees C and shows broad pH optimum between 6.5 and 7.5. In th e absence of Ca2+, only Sr2+ and Ba2+ activate its caseinolytic activi ty, whereas other divalent cations such as Mg2+, Mn2+, Ni2+, Co2+, Cd2 +, Zn2+ and Cu2+ have no effect on its activity. The enzyme undergoes a Ca2+-dependent autolysis in the absence of substrate, producing two main fragments of 50.6 and 31.5 kDa molecular weight, respectively. Pr olonged autolysis results in the complete inactivation of the enzyme.