Myosin isoenzymes in normal and hypertrophied human hearts.

Distinct myosin isoforms were identified from the ventricles and atria of foetal, normal and hypertrophied human hearts. Ventricle and atrium myosins cannot be differentiated by their sedimentation behaviour in the analytical ultracentrifuge, they vary, however, with regard to the Ca2+-dependent ATPase and also the activation parameters in measurements of the enzyme activity in dependence on temperature. In agreement with other authors we observed a foetal light chain in the ventricular tissue of the latter half of gestation, when myosin was characterized by SDS-polyacrylamide gel electrophoresis and isoelectric focusing. Using pyrophosphate gel electrophoresis an additional foetal isomyosin was observed besides the typical ventricular myosin HV-3, which migrates faster. Two distinct myosin isoforms designated as HA-3 and HA-1 occur in the atrium of the normal human heart. It was found that besides their own isoenzymes normal atria also contain ventricular isomyosin, whose relative proportion is markedly increased in the hypertrophic atrium. In contrast, we usually observed only one isoenzyme in the normal ventricle. Moreover, in case of myocardial infarction a dramatic transformation of myosin heavy chain composition with a shift to an atrial myosin type took place in the ventricle.