Effect of diethyl ether on the adenosine triphosphatase activity and the calcium uptake of fragmented sarcoplasmic reticulum of rabbit skeletal muscle
Inesi, G.; Goodman, J.J.; Watanabe, S.
Journal of Biological Chemistry 242(20): 4637-4643
ISSN/ISBN: 0021-9258 PMID: 4228829 Accession: 024540692
Treatment of fragmented preparations of sarcoplasmic reticulum with diethyl ether decreased the C uptake capacity of reticulum, while the ATP-binding capacity as well as the ATP-splitting activity of reticulum were increased. Diethyl ether-treated reticulum preparations retained both the basal and the extra splitting activities of Hasselbach and Makinose, although the latter activity was uncoupled from the C uptake activity. Because the extra splitting of ether-treated reticulum, was not confined in a short period of C uptake process, the following kinetic characteristics at 25[degree] were obtained. In optimal concentration of C, the half-maximal activation of the extra splitting by M was obtained with 0.1 m[image] added MgCl2. Overoptimal concentrations of calcium exerted a competitive inhibition. The plot of the extra splitting activity as a function of ATP concentration showed 2 discrete steps, which suggest 2 different C-dependent activities; their Michaelis-Menten constants were 10[mu][image] and > 1 m[image], and their maximal activities are 1.7 and > 0.6 umoles of phosphate liberated /min/mg of reticulum protein. The ATP splitting by ether-treated preparations of reticulum in the presence of 1, 2-bis-(2-dicarboxy methylaminoethoxy)ethane with no added C, (basal splitting) occurred at ATP concentrations about the same as those for the second step in the extra splitting, but its activity was too small to account for the activity in the 2nd step. C. uptake by nontreated preparations of reticulum also showed 2 steps as the ATP concentration increased; the 1st step occurred at ATP concentrations about 1/10 of those for the ATP-splitting activity mentioned before but the 2nd step occurred at about the same concentrations as those for the ATP splitting.