The dimeric form of Ca2+-ATPase is involved in Ca2+ transport in the sarcoplasmic reticulum.
To identify the functional unit of Ca(2+)-ATPase in the sarcoplasmic reticulum, we assessed Ca(2+)-transport activities occurring on sarcoplasmic reticulum membranes with different combinations of active and inactive Ca(2+)-ATPase molecules. We prepared heterodimers, consisting of a native Ca(2+)-ATPase molecule and a Ca(2+)-ATPase molecule inactivated by FITC labelling, by fusing vesicles loaded with each type of Ca(2+)-ATPase. The heterodimers exhibited neither Ca(2+) transport nor ATP hydrolysis, suggesting that Ca(2+) transport by the Ca(2+)-ATPase requires an interaction between functional Ca(2+)-ATPase monomers. This finding implies that the functional unit of the Ca(2+)-ATPase is a dimer.
Ushimaru
Makoto
M
Department of Chemistry, Kyorin University School of Medicine, Shinkawa 6-20-2, Mitaka, Tokyo, Japan. ushimaru@kyorin-u.ac.jp
Fukushima
Yoshihiro
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D019281:Dimerization; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology* / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*
D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D016650:Fluorescein-5-isothiocyanate; D002118:Calcium