Mn(2+) transport by Ca(2+) -ATPase of sarcoplasmic reticulum.
Ca(2+) -ATPase of sarcoplasmic reticulum is known to pump Mn(2+) in addition to Ca(2+) , but whether its transport mechanism is identical to that of Ca(2+) is ambiguous. To clarify, we examined, by atomic absorption spectroscopy, competition between Mn(2+) and Ca(2+) in active transport using vesicles of sarcoplasmic reticulum (SR). Here, we demonstrate that Ca(2+) -ATPase transports Ca(2+) and Mn(2+) concomitantly but has a much lower affinity for Mn(2+) (apparent Kd ~ 0.5 mm). Stoichiometries of transported ions per ATP hydrolysed, Vmax values and activation energies are very similar. Altogether, Ca(2+) -ATPase appears to use the same mechanism for transporting Mn(2+) as that for Ca(2+) .
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Shin-Ichiro
S
Yonekura
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Chikashi
C
Toyoshima
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D017136:Ion Transport / Q000502:physiology; D008345:Manganese / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*
D008345:Manganese; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
Ca2+-ATPase; ion selectivity; ion transport