title: Limited tryptic digestion of Ca2+,Mg2+-adenosine triphosphatase of the sarcoplasmic reticulum: enzymatic properties of A1b + B complex.
abstract: Sarcoplasmic reticulum membranes were treated with trypsin under conditions leading to accumulation of B and three other fragments a little smaller than A1, namely A1a, A1b, and C (Mr 27,000-28,000) (Saito, K. et al. (1984) J. Biochem. 95, 1297-1304), and enzymatic properties of trypsin-digested ATPase were investigated. The tryptic cleavage pattern of SR membranes in the presence of 1 M glycerol and 5 mM CaCl2 at 35 degrees C was qualitatively similar to that obtained in the presence of Ca2+ alone. However, considerably more A1-derived fragments, A1a and A1b, which are stabilized by the binding of Ca2+ to the enzyme, were accumulated. The sample digested under this condition for 60 min was mainly composed of A1b and B, and was designated as A1b + B complex. ATPase activity was lost in parallel with the formation of A1a and A1b. On the other hand, E-P forming activity was still retained by A1b + B complex. E-P formation with this complex was strictly dependent on the presence of Ca2+ ions at micromolar concentration. This indicates that Ca2+ binding site is well conserved in this complex. E-P formed with A1b + B complex was ADP-sensitive (E1-P), and was not further decomposed, since the transition from E1-P to E2-P was blocked.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology; D010446:Peptide Fragments / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014357:Trypsin / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D010446:Peptide Fragments; D000244:Adenosine Diphosphate; D014357:Trypsin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium