Invariance of stoichiometry of the sarcoplasmic reticulum calcium pump at physiological calcium concentrations--a reevaluation.
The decline of the transport ratio of the sarcoplasmic calcium pump observed in a recent study (A. Gafni and P. D. Boyer, Proc. Natl. Acad. Sci. USA 82, 89-101 [1985] ) results from the retardation of calcium oxalate precipitation at low calcium/protein ratios. The prevailing high internal calcium level supports a rapid calcium backflux and a compensatory ATP hydrolysis during net calcium uptake which reduces the transport ratio. Yet, the determined calcium backflux does not fully account for the decline of the transport ratio. A supposed modulation of the stoichiometry of the pump by external calcium (0.1 microM) is at variance with results of previous studies showing a constant transport ratio of two in the same calcium concentration range.
W
W
Hasselbach
A
A
Migala
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D007473:Ion Channels; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium