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|