ATPase activity of sulfhydryl-modified cardiac myosin from normal and isoproterenol-treated rats

The possible role of sulfhydryl groups in the adaptation of cardiac myosin to work overload has been examined. The functional integrity of sulfhydryl groups was evaluated by measurement of Ca2+- and K+-(EDTA)-ATPase activities of myosins following sulfhydryl modification. No activation of Ca2+-ATPase of normal rat cardiac myosin was observed after pMB or NEM pretreatment. The decrease in Ca2+-ATPase of myosin from hypertrophied hearts was eliminated following sulfhydryl modification: moreover, slight stimulation of Ca2+-ATPase was observed. An increase in KCl concentration did not stimulate the Ca2+-ATPase of NEM-modified myosins obtained from either control or hypertrophied hearts. The sulfhydryl content of rat cardiac myosin expressed as moles of SH per 10(5) g of myosin was 6.99 +/- 0.30 and in IPR-induced hypertrophy did not change it significantly. In the authors' opinion an alteration in the integrity of the sulfhydryl groups may be responsible for the functional partition (decreased Ca2+-ATpase with unchanged K+-[EDTA]-ATPase activity) of myosin from hypertrophied hearts.