title: Procalpain I in cytoplasm is translocated onto plasma and granule membranes during platelet stimulation with thrombin and then activated on the membranes.
abstract: Thrombin stimulation of platelets resulted in changes in the subcellular localization of calpain I, with a concomitant alteration of its molecular weight as measured by immunoblotting. Calpain I in resting platelets was distributed as procalpain I, an 80 kDa form which does not exhibit the enzyme activity, and 83% of the total antigen was localized in the cytosol fraction. When platelets were stimulated with thrombin, the total content of calpain I antigen was not significantly changed as compared with that of the resting platelets, though a decrease in the cytosolic distribution of 80 kDa form (from 83% to 47% of the total antigen) was observed with concomitant appearance of the active 76 kDa and intermediate 78 kDa forms of calpain I and increase in the 80 kDa form in the granule and membrane fractions. These results indicated that calpain I was translocated from the cytosol to both the plasma and granule membranes as procalpain I and then activated on the membranes during platelet stimulation with thrombin.
authors.affiliation: Department of Clinical Biochemistry, Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kuboki
authors.forename: H
authors.initials: H
authors.lastname: Ishii
authors.forename: S
authors.initials: S
authors.lastname: Horie
authors.forename: M
authors.initials: M
authors.lastname: Kazama
mesh_terms: D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D002154:Calpain / Q000097:blood* / Q000302:isolation & purification; D003594:Cytoplasmic Granules / Q000201:enzymology*; D003600:Cytosol / Q000201:enzymology; D004792:Enzyme Precursors / Q000097:blood* / Q000302:isolation & purification; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology; D007770:L-Lactate Dehydrogenase / Q000097:blood / Q000302:isolation & purification; D008970:Molecular Weight; D013917:Thrombin / Q000494:pharmacology*
chemical_list: D004792:Enzyme Precursors; D007770:L-Lactate Dehydrogenase; D013917:Thrombin; D002154:Calpain; C098484:mu-calpain proenzyme