title: Correlation between lipid fluidity and tryptic susceptibility of Ca2+-ATPase in sarcoplasmic reticulum membranes.
abstract: Lipid fluidity in native and denatured sarcoplasmic reticulum membranes and extracted lipids was monitored between -30 and 30 degrees C using trans-parinaric acid as a fluorescent probe. In addition to a large increase in fluidity between -30 and 0 degree C in each system, a phase change centered near 10 degrees C was observed in the extracted lipids but not in either the native or denatured membranes. A significant change in fluorescence intensity near 15 degrees C was observed in native sarcoplasmic reticulum membranes, however, when trans-parinaric acid was excited by energy transfer from tryptophan residues of the membrane protein. When Ca2+-ATPase was subjected to proteolytic cleavage by trypsin as a function of temperature, a change in susceptibility was detected at about 15-20 degrees C in the native membranes but not in a solubilized preparation. It is proposed that one or more structural changes in the microenvironment of Ca2+-ATPase in the native membrane occur between 15 and 20 degrees C which may be related to the change in apparent activation energy which is observed for this enzyme.
authors.forename: J
authors.initials: J
authors.lastname: Blazyk
authors.forename: C J
authors.initials: CJ
authors.lastname: Wu
authors.forename: S C
authors.initials: SC
authors.lastname: Wu
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004735:Energy Transfer; D005453:Fluorescence; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012995:Solubility; D013696:Temperature; D014357:Trypsin / Q000378:metabolism*
chemical_list: D008563:Membrane Lipids; D014357:Trypsin; D000252:Calcium-Transporting ATPases