title: Ca2+-ATPase membrane crystals in sarcoplasmic reticulum. The effect of trypsin digestion.
abstract: Vanadate induces the formation of two-dimensional crystalline arrays of Ca2+-ATPase molecules in sarcoplasmic reticulum. The Ca2+-ATPase membrane crystals are evenly distributed among the terminal cisternae and longitudinal tubules of sarcoplasmic reticulum, but very few crystals were observed in the T tubules. Tryptic cleavage of the Ca2+ transport ATPase into two major fragments (A and B) did not interfere with the vanadate-induced formation of membrane crystals. The ability of Ca2+-ATPase to crystallize was lost after further cleavage of the A fragment into the A1 and A2 subfragments that is known to be accompanied by loss of Ca2+ uptake. Vanadate (0.1-5 mM) inhibited the secondary cleavage of Ca2+-ATPase by trypsin suggesting that the susceptibility of the tryptic cleavage sites is influenced either by the conformation of the enzyme or by the formation of ATPase crystals.
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000032:analysis* / Q000378:metabolism; D003460:Crystallization; D008566:Membranes / Q000032:analysis; D008854:Microscopy, Electron; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014357:Trypsin / Q000378:metabolism*; D014639:Vanadium / Q000494:pharmacology
chemical_list: D014639:Vanadium; D014357:Trypsin; D000252:Calcium-Transporting ATPases