The incorporation of [14C] N-ethylmaleimide reveals fast and slow-reacting sulfhydryl groups in sarcoplasmic reticulum. Two proteins react with the label: a fast-reacting glycoprotein recently isolated (Ikemoto, Cucchiaro and Garcia (1976) J. Cell Biol.70, 290a), and the Ca2+-ATPase. Labeling sarcoplasmic reticulum with a maleimide spin label gives a similar pattern. The spectra of maleimide-spin-labeled sarcoplasmic reticulum have both 'strongly' and 'weakly' immobilized components. Maleimide-spin-labeled purified Ca2+-ATPase, or sarcoplasmic reticulum labeled first with N-ethylmaleimide, and then with maleimide spin label, show spectra devoid of the 'weakly' immobilized component; the latter is enhanced in partially purified glycoprotein obtained from spin-labeled sarcoplasmic reticulum. This indicates that spectra from maleimide-spin-labeled sarcoplasmic reticulum do not reflect exclusively the state of the Ca2+-ATPase enzyme.
|Original language||English (US)|
|Number of pages||8|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - Oct 24 1977|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS: The authors wish to thank Drs. N. Ikemoto and J. Gergely for their kind criticism of the manuscript. The research was supported by grants from the American Heart Association (74913), NIH (AM 16922, HL-05811 and HL-059491, NSF, and the Muscular Dystrophy Association of America, Inc. During the course of this research D.D.T. was a Postdoctoral Fellow of the Muscular Dystrophy Association of America, Inc.