In this article the morphology of sarcoplasmic reticulum, classification of Ca2+-ATPase (SERCA) isoenzymes presented in this membrane system, as well as their topology will be reviewed. The focus is on the structure and interactions of Ca2+-ATPase determined by electron and X-ray crystallography, lamellar X-ray and neutron diffraction analysis of the profile structure of Ca2+-ATPase in sarcoplasmic reticulum multilayers. In addition, targeting of the Ca2+-ATPase to the sarcoplasmic reticulum is discussed.
In this review the molecular characteristics and reaction mechanisms of different Ca2+ transport systems associated with various membranes in muscle cells will be summarized. The following topics will be discussed in detail: a brief history of early observations concerning maintenance and regulation of cellular Ca2+ homeostasis, characterization of the Ca2+ pumps residing in plasma membranes and sarco(endo)plasmic reticulum, mitochondrial Ca2+ transport, Ca2+-binding proteins, coordinated expression of Ca2+ transport systems, a general background of muscle excitation-contraction coupling with emphasis to the calcium release channels of plasma membrane and sarcoplasmic reticulum, the structure and function of dihydropyridine and ryanodine receptors of skeletal and cardiac muscles, and finally their disposition in various types of muscles.
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