Comparison of Mg2+ vs Ca2+, K+ and actin-activation of myosin after trinitrophenylation.
While modification of six lysyl residues causes a near maximal decrease in Ca2+, K+, and actin + Mg2+ -activated myosin ATPase activities in rabbit skeletal muscle myosin, it takes nearly twice this number of modified lysyl groups to cause a similar alteration in canine cardiac myosin where trinitrophenylation is nonspecific. It appears that there are several rapidly reacting lysyl residues in cardiac myosin;  the active site of cardiac myosin is protected by ATP after modification of a limited number of these rapidly reacting lysyl groups. In both myosins, after a charge modification of these rapidly reacting lysyl groups, 6 in rabbit skeletal muscle myosin and 10 in canine cardiac myosin, there is a decrease in Ca2+, K+, and actin + Mg2+ -stimulation of myosin but an activation of Mg2+ -stimulated myosin ATPase activity, thus making actin + Mg2+ -stimulated myosin ATPase activity more like activation with K+ or Ca2+ as compared to activation with Mg2+ alone.
D000199:Actins / Q000494:pharmacology*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology*; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D011817:Rabbits; D014301:Trinitrobenzenes / Q000138:chemical synthesis
D000199:Actins; D014301:Trinitrobenzenes; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium; D011188:Potassium; D002118:Calcium