title: Reversible activation of human neutrophil calpain promoted by interaction with plasma membranes.
abstract: Human neutrophil calpain is a monomer of 85 kDa molecular weight. The proteinase shows an absolute requirement for Ca2+ with maximal catalytic activity at 0.1-0.2 mM Ca2+ and negligible activity at 1-5 microM Ca2+. At this concentration of Ca2+ neutrophil calpain becomes active and reaches 65% of its maximal catalytic activity following interaction with plasma membranes. The activation is fully reversible since the enzyme returns to its native, high Ca2+ requiring form following removal of the membranes. Membrane phospholipids appear to be the physiological compounds responsible for the promotion of such reversible activation. Unlike other Ca2+ dependent proteinases, neutrophil calpain does not undergo conversion to a low Ca2+ requiring form by limited autoproteolysis.
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002154:Calpain; D002384:Catalysis; D010450:Endopeptidases / Q000097:blood*; D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008563:Membrane Lipids / Q000097:blood / Q000502:physiology*; D008970:Molecular Weight; D009504:Neutrophils / Q000201:enzymology*; D010743:Phospholipids / Q000097:blood / Q000502:physiology*
chemical_list: D008563:Membrane Lipids; D010743:Phospholipids; D010450:Endopeptidases; D002154:Calpain; D002118:Calcium