title: The hydrophilic domain of phospholamban inhibits the Ca(2+)-ATPase--the importance of the method of assay.
abstract: The peptide MEKVQYLTRSAIRRASTIEMPQQAR-Cys representing residues 1-25 of phospholamban (PLN) decreases by 40% the maximal state rate of ATP hydrolysis by the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum (SR), measured at saturating concentrations of Ca2+. The pattern of Ca2+ uptake by SR vesicles in the presence of oxalate is complex, with an initial fast phase being followed by a lag phase and a second, slower phase of Ca2+ accumulation. PLN(1-25) reduces the rate of the slower phase of Ca2+ accumulation by 30%. However, if the level of accumulation of Ca2+ is measured after 2 min., the effect of PLN(1-25) is much less marked. It is concluded that PLN(1-25) inhibits the ATPase, but that the effects of this inhibition are not apparent under some assay conditions.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000037:antagonists & inhibitors*; D004396:Coloring Agents; D007700:Kinetics; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology*; D009282:Naphthalenesulfonates; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D015203:Reproducibility of Results; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013053:Spectrophotometry / Q000379:methods; D013997:Time Factors; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D004396:Coloring Agents; D009282:Naphthalenesulfonates; D010446:Peptide Fragments; D000099211:Phospholamban; C016238:antipyrylazo III