title: Decreased conformational stability of the sarcoplasmic reticulum Ca-ATPase in aged skeletal muscle.
abstract: Sarcoplasmic reticulum (SR) membranes purified from young adult (4-6 months) and aged (26-28 months) Fischer 344 male rat skeletal muscle were compared with respect to the functional and structural properties of the Ca-ATPase and its associated lipids. While we find no age-related alterations in (1) expression levels of Ca-ATPase protein, and (2) calcium transport and ATPase activities, the Ca-ATPase isolated from aged muscle exhibits more rapid inactivation during mild (37 degrees C) heat treatment relative to that from young muscle. Saturation-transfer EPR measurements of maleimide spin-labeled Ca-ATPase and parallel measurements of fatty acyl chain dynamics demonstrate that, accompanying heat inactivation, the Ca-ATPase from aged skeletal muscle more readily undergoes self-association to form inactive oligomeric species without initial age-related differences in association state of the protein. Neither age nor heat inactivation results in differences in acyl chain dynamics of the bilayer including those lipids at the lipid-protein interface. Initial rates of tryptic digestion associated with the Ca-ATPase in SR isolated from aged muscle are 16(+/- 2)% higher relative to that from young muscle. indicating more solvent exposure of a portion of the cytoplasmic domain. During heat inactivation these structural differences are amplified as a result of immediate and rapid further unfolding of the Ca-ATPase isolated from aged muscle relative to the delayed unfolding of the Ca-ATPase isolated from young muscle. Thus age-related alterations in the solvent exposure of cytoplasmic peptides of the Ca-ATPase are likely to be critical to the loss of conformational and functional stability.
authors.affiliation: Department of Biochemistry, University of Kansas, Lawrence 66045-2106, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Ferrington
authors.forename: T E
authors.initials: TE
authors.lastname: Jones
authors.forename: Z
authors.initials: Z
authors.lastname: Qin
authors.forename: M
authors.initials: M
authors.lastname: Miller-Schlyer
authors.forename: T C
authors.initials: TC
authors.lastname: Squier
authors.forename: D J
authors.initials: DJ
authors.lastname: Bigelow
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000648:ultrastructure; D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D008297:Male; D008563:Membrane Lipids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011916:Rats, Inbred F344; D012519:Sarcoplasmic Reticulum / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D008563:Membrane Lipids; D000252:Calcium-Transporting ATPases; D002118:Calcium