Cooperative binding of calcium to glycerinated skeletal muscle fibers |
| |
Authors: | Franklin Fuchs Margaret Bayuk |
| |
Institution: | Department of Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pa. 15261 U.S.A. |
| |
Abstract: | The binding of 45Ca2+ to glycerinated rabbit psoas fibers was measured by means of a double isotope technique. With 5 mM Mg2+ (no ATP) binding was half-maximal at 1.4 · 10?6M Ca2+ and the maximal amount bound was 1.6 μmol/g protein. At < 50% saturation, the Scatchard plot had a positive slope and the Hill coefficient was 2.2. At greater than 50% saturation, the Scatchard plot was linear with a negative slope (K′ = 0.8 · 106 M?1) and the Hill coefficient was 1.0. In the absence of Mg2+, binding was half-maximal at 3 · 10?7 M Ca2+ and the maximal amount bound was 2.9 μmol/g protein. The Scatchard plot indicated two classes of sites with K′ values of about 2 · 107 and 2 · 106 M?1. The Hill coefficient in the mid-saturation range was approx. 0.6. The data indicate that in the presence of Mg2+ binding to about half of the total Ca2+ binding sites is suppressed and there is a strong positive cooperativity involving half of the remaining sites. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|