Transient kinetics of a Ca2+-induced fluorescence change from membrane-associated and solubilized sarcoplasmic reticulum Ca2+-ATPase.
The kinetics and extent of the fluorescence change induced by Ca2+ interaction with the Ca2+-ATPase from sarcoplasmic reticulum have been compared by stopped flow fluorimetry for three preparations: sarcoplasmic reticulum; purified ATPase in membrane vesicles; and solubilized, delipidated ATPase. The kinetics of Ca2+ release and binding for both purified preparations could be described by a single exponential as has been observed for sarcoplasmic reticulum. The rate and extent of the fluorescence change for the solubilized and membrane-associated preparations are shown to be quite similar to those of the sarcoplasmic reticulum. From these results, it is concluded that all of the Ca2+-induced fluoescence change in sarcoplasmic reticulum originates from the Ca2+-ATPase. In addition, since the change in fluorescence is probably result of a conformational change in the ATPase during the Ca2+ pumping cycle, the results provide additional evidence that monomeric Ca2+-ATPase may be capable of Ca2+ transport since the delipidated preparation is monomeric under the conditions used for these experiments. Finally, it is concluded that phospholipid bilayer is not essential for this conformational change.
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D005453:Fluorescence; D007700:Kinetics; D011487:Protein Conformation / Q000187:drug effects; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D000252:Calcium-Transporting ATPases; D002118:Calcium