Identification, kinetic properties and intracellular localization of the (Ca(2+)-Mg2+)-ATPase from the intracellular stores of chicken cerebellum.
The microsomal fraction of chicken cerebellum expresses a large amount of Ca(2+)-ATPase (105 kDa), which is phosphorylated by ATP in the presence of Ca2+. The Ca(2+)-ATPase activity is highly sensitive to temperature and to the presence of detergents. This ATPase has kinetic properties similar to those of chicken skeletal-muscle sarcoplasmic reticulum, as (i) it is activated by low (microM) and inhibited by high (mM) Ca2+ concentrations, (ii) it shows biphasic activation with ATP and (iii) it is inhibited by vanadate. However, the vanadate-sensitivity is at least 10 times greater than that observed in chicken skeletal or cardiac sarcoplasmic-reticulum Ca(2+)-ATPases. Thus, despite cross-reacting with antibodies against the cardiac and skeletal isoforms, the cerebellar microsomal Ca(2+)-ATPase appears to be distinct from both muscle enzymes. The Ca(2+)-ATPase is concentrated in, but not exclusive to, Purkinje neurons. In Purkinje neurons the Ca(2+)-ATPase appears to be expressed throughout the cell body, the dendritic tree (and the spines) and the axons. At the electron-microscope level the Ca(2+)-ATPase is found in smooth and rough endoplasmic-reticulum cisternae as well as in other, yet unidentified, smooth-surfaced structures.
Michelangeli
F
F
Institute of General Pathology, University of padova, Italy.
Di Virgilio
F
F
Villa
A
A
Podini
P
P
Meldolesi
J
J
Pozzan
T
T
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002531:Cerebellum / Q000201:enzymology* / Q000648:ultrastructure; D002645:Chickens; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008854:Microscopy, Electron; D008861:Microsomes / Q000201:enzymology; D009132:Muscles / Q000201:enzymology; D011689:Purkinje Cells / Q000201:enzymology / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D014638:Vanadates / Q000494:pharmacology
D014638:Vanadates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium