Comparisons of rat cardiac myosins at fetal stages in young animals and in hypothyroid adults.

Rat cardiac ventricular myosins were obtained from fetuses, from young normal animals, and from hypophysectomized adults. The purified proteins were compared by several techniques: (i) electrophoresis in non-denaturing conditions (pyrophosphate buffer), (ii) one- and two-dimensional analysis after proteolytic cleavage, (iii) immunological blotting after electrophoretic purification, and (iv) competitive enzyme-linked immunosorbent assay. Antibodies specific to each of the two major isoenzymes of adult rat heart (V1 and V3 according to the terminology of Hoh et al. (Hoh, J. F. Y., McGrath, P. A., and Hale, P. T. (1978) J. Mol. Cell. Cardiol. 10, 1053-1076) were used for the immunological studies. The heavy chains of the ventricular myosin isoenzymes of fetuses (V3F) were indistinguishable from those of the V3H isoenzyme present in hypophysectomized adults; both proteins differed from the V1 isoform of young animals. The light chains of V3F, V3H, and V1 were the same, except that V3F contained in addition a small amount of the embryonic light chain (Whalen, R. G., and Sell, S. M. (1980) Nature 286, 731-733). These results strongly suggest that adaptation of the adult rat heart to the hormonal deficiencies of hypophysectomy is mediated by the synthesis of the same myosin heavy chain form which is predominant in fetal hearts.