Human cardiac myosin ATPase and light subunits. A comparative study.

Myosin was extracted from normal human hearts (autopsy material) and compared to that of pig heart and rabbit white skeletal muscle. Myosin light subunits were isolated by a preparative urea gel electrophoresis. These subunits were shown by urea and sodium dodecylsulfate gel electrophoresis to be only slightly affected by the time lapse between death and the beginning of myosin extraction. This was also true for myosin ATPases. The Ca-2+-activated ATPases of pig and human heart myosins have the same apparent Km and V, whereas white skeletal muscle myosin ATPase has the same Km with a higher V. Human myosin light subunits, when compared to those of pig heart possess: (i) different molecular weights: 27 999 and 18 000 datlons for pig heart, and 25 000 and 19 000 daltons for human heart. (ii) for both the light chains, different ultraviolet spectra and a higher helical content for the subunit molecular weight 25 000. (iii) a different composition for several amino acids (Tyr, Pro, Lys). A third light subunit (molecular weight 15 000) was occasionally seen in human as well as pig heart myosin. It concentration varied inversely with that of the subunit molecular weight 27 000-25 000, and so was probably a degradation product of the heaviest subunit.