Sacroplasmic reticulum

Site specific mutagenesis of sacroplasmic reticulum -ATPase... 

Calsequestrin is a calcium-storage protein found in the sacroplasmic reticulum, which binds about 50 calcium ions per monomer (molecular weight 40 000) with binding constants in the range 103-105 dm3 mol. Release and uptake of Ca2+ during muscle contradion and relaxation involve this store. Calsequestrin from rabbit skeletal muscle has a random coil conformation in the absence of calcium. Binding of Ca2+ is associated with a change to a more compact structure.267... 

As noted earlier, the discussion of excitable membranes in Chapter 13 incorporates the detailed stmctures of an ion channel (the prokaryotic potassium channel) and an ion pump (the sacroplasmic reticulum calcium ATPase). Figure 9.21... 

Ion channels are found not only in the cell membrane but also in the membranes of the intracellular organelles such as mitochondria, lysozymes, nucleus, and secretory, endocytotic, and synaptic vesicles, as well as in the endoplasmic/sacroplasmic reticulum (ER/SR). Two major intracellular Ca channels, the inositol 1,4,5-trisphosphate (IP3) receptor and the ryanodine receptor (RyR), are located in the ER/SR membranes and contribute to changes in intracellular Ca concentration. Based on their mechanism of activation, these two channels are classified as ligand-gated channels (Section 16.4.1). 

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