title: Membrane crystals of Ca2+-ATPase in sarcoplasmic reticulum of fast and slow skeletal and cardiac muscles.
abstract: Crystalline arrays of Ca2+ transport ATPase develop in sarcoplasmic reticulum membranes after treatment with Na3VO4 in a calcium-free medium [ Dux , L. and Martonosi , A. (1983) J. Biol. Chem. 258, 2599-2603]. The proportion of vesicles containing Ca2+-ATPase crystals in microsome preparations isolated from rat muscle of different fiber types (semimembranosus, levator ani, extensor digitorum longus, diaphragm, soleus, and heart) correlates well with the Ca2+-ATPase content and Ca2+-modulated ATPase activity. This implies that the concentration of Ca2+-ATPase in sarcoplasmic reticulum membranes of fast and slow skeletal or cardiac muscles differs only slightly, and the low Ca2+ transport activity of 'sarcoplasmic reticulum' preparations isolated from slow-twitch skeletal and cardiac muscles is due to the presence of large amount of non-sarcoplasmic-reticulum membrane elements. This is in accord with the relatively small differences in the density of 8.5-nm intramembranous particles seen by freeze-etch electron microscopy in sarcoplasmic reticulum of red and white muscles. The dimensions of the Ca2+-ATPase crystal lattice are similar in sarcoplasmic reticulum membranes of different fiber types; therefore if structural differences exist between 'isoenzymes' of Ca2+-ATPase, these are not reflected in the crystal-lattice.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D008297:Male; D008861:Microsomes / Q000201:enzymology / Q000648:ultrastructure; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000201:enzymology* / Q000648:ultrastructure; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D014639:Vanadium; D014638:Vanadates; D000252:Calcium-Transporting ATPases; D002118:Calcium