Structural and Enzymatic Comparison of Human Cardiac Muscle Myosins Isolated from Infants, Adults, and Patients with Hypertrophic Cardiomyopathy

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Abstract

Human cardiac ventricular myosins were prepared from autopsy samples from nine adults, seven infants, and from surgical specimens from seven patients undergoing left ventricular septal myectomy for obstructive hypertrophic cardiomyopathy. Infant myosin differed from adult myosin in two important characteristics: (a) ∼30% of the 27,000-dalton myosin light chain is replaced by a 28,000-dalton light chain, and (b) the actin-activated myosin MgATPase activity of infant myosin is significantly lower than that of adult myosin (64 nmol phosphate released/mg myosin per min vs. 124 nmol/mg per min at 37°C). The K+-EDTA ATPase activity of the myosin measured in 0.5M KCl is also lower in infants (1,210 nmol/mg per min vs. 620 nmol/mg per min at 37°C), but the Ca++-activated ATPase is not significantly different. There were no differences in enzymatic activity between the normal adult and cardiomyopathic myosins.

Authors

John J. Schier, Robert S. Adelstein