Luminal dissociation of Ca2+ from the phosphorylated Ca2+-ATPase is sequential and gated by Mg2

• Published in: Biochemical journal 1999-04, Vol.339 ( Pt 2) (2), p.351-357
• Main Authors: Duggleby, R C, East, M, Lee, A G
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Calcium - metabolism; Calcium-Transporting ATPases - antagonists & inhibitors; Calcium-Transporting ATPases - chemistry; Calcium-Transporting ATPases - metabolism; Ion Transport; Kinetics; Magnesium - metabolism; Molecular Sequence Data; Muscle, Skeletal - enzymology; Phosphorylation; Rabbits
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3390351

Transport of Ca2+ across the membrane by the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum involves the transfer of two Ca2+ ions from a pair of cytoplasmic sites to a pair of luminal sites, driven by phosphorylation of the ATPase. The ATPase is inhibited by Mg2+ at alkaline pH values. Inhibition follows from a decrease in the rate of release of Ca2+ from the phosphorylated ATPase. Phosphorylation-induced release of Ca2+ from the ATPase is biphasic at alkaline pH, which is consistent with sequential release of Ca2+ from the phosphorylated ATPase; the rates of both components decrease with increasing Mg concentration. The effect of Mg2+ on the slow phase of release follows from the binding of Mg2+ at the empty outer luminal site, vacated by the release of the first Ca2+ ion. The effect of Mg2+ on the rate of release of the first Ca2+ ion could follow from binding to a gating site also affecting the binding of Ca2+ to the cytoplasmic sites.