Functional integrity of the SH1 site in myosin from hypertrophied myocardium.
The hypothesis that an alteration in the SH1 site of hypertrophy myosin is reponsible for the reduced Ca2+-stimulated ATPase activity is examined.The functional integrity of the SH1 site was evaluated by measurement of the (K+)-EDTA-stimulated and Mg2+-inhibited ATPase activities. Neither activity differed from control although the Ca2+-stimulated ATPase of the same preparations was significantly reduced. The reduction in Ca2+-activated ATPase was independent of ionic strength. Titration with N-ethylmaleimide elevated the Ca2+-stimulated ATPase of hypertrophy myosin to the same peak activity as control. Actin-stimulated ATPase activity of hypertrophy myosin was also reduced. The results indicate that the SH1 of hypertrophy myosin is functionally intact for (K+)EDTA-stimulated ATPase and Mg2+ inhibition, but functionally deficient with regard to Ca2+-stimulated and actin-activated ATPase activities. This implies a partition of the functional aspects of SH1.
D000199:Actins; D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D006332:Cardiomegaly / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000032:analysis
D000199:Actins; D013438:Sulfhydryl Compounds; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium; D005033:Ethylmaleimide; D002118:Calcium