Phosphodiesterase activator protein and troponin C have been purified from rat testis and rabbit skeletal muscle, respectively. The 2 proteins appear to be structurally distinct since the activator protein migrates faster than troponin C on sodium dodecyl sulfate polyacrylamide gels. Each of the calcium binding proteins will, however, substitute for the other in their respective biological systems. Testis activator protein forms a complex with rabbit muscle troponin subunits TnI and TnT soluble in low salt. This hybrid complex (AIT) can regulate rabbit skeletal muscle actomyosin ATPase activity. AIT regulation, although influenced by free Ca2+ levels, is distinct from that of native troponin. Likewise, muscle troponin C can substitute for activator protein in the stimulation of cyclic nucleotide phosphodiesterase. Troponin C will fully stimulate phosphodiesterase although its affinity is 600 fold lower than that of activator protein. Ca2+ regulation studies demonstrate that both proteins require micromolar levels of free Ca2+ to induce phosphodiesterase activation. Activator protein requires 1.2x10-6M and troponin-C, 1.9x10-6M free Ca2+ for half-maximal stimulation of phenodiesterase. The biological cross-reactivity of these proteins supports the sequence homology recently reported by Watterson et al. (Watterson, D.M., Harrelson, W.G., Keller, P.M., Sharief, F., and Vanaman, T.C. (1976) J. Biol.Chem. 251, 4501-4513). In addition, this preliminary study suggests that this nonmuscle troponin-C-like protein potentially may function in other Ca2+-regulated cellular events in addition to its modulation of cyclic nucleotide levels.
|Original language||English (US)|
|Number of pages||4|
|Journal||Journal of Biological Chemistry|
|State||Published - 1977|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology