| Abstract: | Mixed anhydrids of AMP, ADP, ATP and IMP and mesitylene carboxylic acid (AMP-MC, ADP-MC, ATP-MC and IMP-MC) are efficient irreversible inhibitors of the Ca-ATPase activity of myosin and heavy meromyosin. The highest rate of inhibition is observed in the case of AMP-MC: at AMP-MC concentration of 1,5.10(-3) M the half inactivation time for heavy meromyosin varies in different protein preparations from 10 to 20 min. The rates of inhibition in the presence of ADP-MC and ATP-MC are roughly the same and are far lower than those for AMP-MC (half inactivation time is 1,5-2 hrs). However, in the latter case the inhibition is complete, the time of the analogs interaction with the protein being increased up to several hours. In the presence of IMP-MC the inhibition is also time-dependent but is never complete. A necessary condition for the manifestation of irreversible inhibition of the Ca-ATPase activity of TMM by phosphorylating analogs of the substrate is the presence of bivalent cations. No inhibition occurs in the presence of EDTA. An addition of ADP or ATP to the preincubation medium causes a sharp decrease of the inhibition rate (a protective effect), which suggests a specific interaction of the analogs with TMM at the substrate binding site. |
