title: Activation by hemoglobin of the Ca2+-requiring neutral proteinase of human erythrocytes: structural requirements.
abstract: The proenzyme form of the Ca2+-requiring neutral proteinase of human erythrocytes (procalpain) is converted to the active proteinase (calpain) by low concentrations of Ca2+ in the presence of appropriate substrates such as beta-hemoglobin or heme-free beta-globin chains. Modification of these substrates by limited proteolysis with calpain abolishes their ability to promote the conversion of procalpain. A similar requirement for the presence of unmodified beta-hemoglobin or heme-free beta-globin chains is observed for the autocatalytic inactivation of calpain. The conversion of procalpain to calpain is accompanied by a small decrease in the molecular mass of the catalytic subunit, from 80 kDa to 75 kDa; however, the activation is not accelerated by the addition of a small quantity of calpain. The autocatalytic inactivation of active CANP is related to the disappearance of the 75 kDa subunit and the formation of smaller peptide fragments.
mesh_terms: D002154:Calpain; D010450:Endopeptidases / Q000097:blood*; D004789:Enzyme Activation; D004912:Erythrocytes / Q000201:enzymology*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight
chemical_list: D006454:Hemoglobins; D046911:Macromolecular Substances; D010450:Endopeptidases; D002154:Calpain