Modification of the Rapidly Reacting Thiols of Atrial and Ventricular Myosins

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Abstract
Environmental variances were noted around the rapidly reacting SH‐1 thiol of ventricular versus atrial myosin, based on electron paramagnetic resonance studies. Further studies, in which either SH‐1 or SH‐1 +SH‐2 thiols were modified with N‐ethylmaleimide, indicated the importance of the SH‐2 moiety of both isozymes for gcneration of tension, when analyzed as synthetic actomyosin threads. Comparative EPR studies showed that the spin label was more strongly immobilized when complexed to ventricular SH‐1 thiol as compared to when it was complexed to atrial myosin. Likewise, addition of PP1, ATP or ADP created a greater mobility in the spin label when added to ventricular spin‐labeled myosin as compared to that of atrial myosin. Comparative studies of spin‐labeled actomyosin versus myosin analyzed at different EPR power settings also demonstrated disparaties surrounding the SH‐1 thiol between the two myosin isozymes.