title: Identification of low-Ca2+- and high-Ca2+-requiring neutral proteases in rat retina.
abstract: Two low-Ca2+-requiring proteases (calpain I) and one high-Ca2+-requiring protease (calpain II) have been separated from the cytosol of rat retina by DEAE-cellulose column chromatography. Calpain I was half-maximally activated at 3 microM free Ca2+ and fully activated at 10 microM free Ca2+. Half-maximal activation of calpain II was at 0.4 mM free Ca2+ while full activation was observed at 0.8 mM free Ca2+. Calpain activity has also been demonstrated in sealed rod outer segments. The soluble fraction of the rod outer segments contained 89% of the enzyme activity. The possible role of calpain in retina is discussed.
authors.forename: P K
authors.initials: PK
authors.lastname: Tsung
authors.forename: J B
authors.initials: JB
authors.lastname: Lombardini
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002154:Calpain; D002848:Chromatography, DEAE-Cellulose; D003600:Cytosol / Q000201:enzymology; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000201:enzymology*; D012374:Rod Cell Outer Segment / Q000201:enzymology
chemical_list: D010450:Endopeptidases; D002154:Calpain; D002118:Calcium