Effect of Ca2+ on the dimeric structure of scallop sarcoplasmic reticulum.
J Cell Biol
; 108(2): 511-20, 1989 Feb.
Article
em En
| MEDLINE
| ID: mdl-2521860
ABSTRACT
Scallop sarcoplasmic reticulum (SR), visualized in situ by freeze-fracture and deep-etching, is characterized by long tubes displaying crystalline arrays of Ca2+-ATPase dimer ribbons, resembling those observed in isolated SR vesicles. The orderly arrangement of the Ca2+-ATPase molecules is well preserved in muscle bundles permeabilized with saponin. Treatment with saponin, however, is not needed to isolate SR vesicles displaying a crystalline surface structure. Omission of ATP from the isolation procedure of SR vesicles does not alter the dimeric organization of the Ca2+-ATPase, although the overall appearance of the tubes seems to be affected the edges of the vesicles are scalloped and the individual Ca2+-ATPase molecules are not clearly defined. The effect of Ca2+ on isolated scallop SR vesicles was investigated by correlating the enzymatic activity and calcium-binding properties of the Ca2+-ATPase with the surface structure of the vesicles, as revealed by electron microscopy. The dimeric organization of the membrane is preserved at Ca2+ concentrations where the Ca2+ binds to the high affinity sites (half-maximum saturation at pCa approximately 7.0 with a Hill coefficient of 2.1) and the Ca2+-ATPase is activated (half-maximum activation at pCa approximately 6.8 with a Hill coefficient of 1.84). Higher Ca2+ concentrations disrupt the crystalline surface array of the SR tubes, both in the presence and absence of ATP. We discuss here whether the Ca2+-ATPase dimer identified as a structural unit of the SR membrane represents the Ca2+ pump in the membrane.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Retículo Sarcoplasmático
/
Cálcio
/
ATPases Transportadoras de Cálcio
/
Moluscos
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Ano de publicação:
1989
Tipo de documento:
Article