An additional low molecular weight subunit in purified preparations of myosin from hypertrophied myocardium

Comparative sequence of myosin light chains from normal and hypertrophied human hearts

Myosin light chains from normal and hypertrophied human hearts were partially sequenced in order to see whether structural modifications of these light subunits could provide a molecular basis for the changes observed in heart properties and in myosin enzymatic activity. Normal light chains were prepared form hearts taken at autopsy, weighing 350 g or less and apparently devoid of myocardial disease. "Hypertrophied cardiac myosin light chains" were prepared from two greatly hypertrophied hearts, weighing 600 and750 g. No amino acid substitutions, deletions, or additions were observed in the light chains from hypertrophied hearts. The third light chain previously reported in human cardiac myosin and related to hypertrophy was found to be a proteolytic product of LC2. The comparison between human and beef cardiac myosin light chains indicated that the sequences of these subunits of the myosin molecule are highly conserved.

Cardiac contractile proteins. Adenosine triphosphatase activity and physiological function

This review has pointed out the good correlation frequently observed between ATPase activity of various contractile protein preparations and contractile function of various muscles including the myocardium. Some of the variables in the measurement of the various ATPases and the relationship of these measurements to physiological ATPase in the intact myofibril have been mentioned. The possible roles of changes in the light chains of sulfhydryl groups in the control of ATPase activity have been outlined. The possibility that phosphorylating reactions might exert control over physiological activity remains to be clarified. It is evident that, despite the large amount of research that has been done, our understanding of how the biochemistry of contractile proteins relates to physiological function is in its infancy, and only with a more complete elucidation of the underlying biochemistry of the components of contractile proteins of physiological and pathophysiological adaptations become evident.

The amino acid composition of actin and myosin and Ca2+-activated myosin adenosine triphosphatase in chronic canine congestive heart failure

The Ca2+-activated myosin ATPase and the amino acid compositions of actin and myosin were determined for preparations from chronically failing dog hearts. Hypertrophy and congestive heart failure were produced by combined tricuspid valve insufficiency and pulmonary artery stenosis. Control, shamoperated, and noncardiac circulatory failure (inferior vena cava constriction) dogs also were studied. All hearts were divided into right ventricle, septum and left ventricle and each sample was individually analyzed. Calcium-activated ATPase decreased in the failing hearts and showed a distinct gradient of depression from right to left ventricles. There were no changes in ATPase activity among the other groups. The amino acid composition of actin was the same regardless of origin. The amino acid composition of myosin was unaltered except that cystine/2 residues were markedly decreased in failing heart myosin. The same gradient of depression was present as was found for Ca2+-activated myosin ATPase. This study suggests that protein metabolism is abnormal and that altered proteins are produced in hypertrophy and congestive heart failure. It appears that these changes do not affect all proteins, since actin was normal by the parameters studied. It is clear that the stressed ventricle is the most severely involved, but the entire heart is altered to some degree. Thus, we conclude that altered protein metabolism may be an important primary factor in the genesis of heart failure.