A comparative study of skeletal and cardiac tropomyosins

Summary The subunit composition, the thiol group content and the biological activities of cardiac tropomyosin (TM) of various animal species were compared. Cardiac TM from small animals such as rabbit, guinea-pig, rat and dog contain 2 SH/mole and were resolved into one band on SDS and acid urea electrophoresis and into two bands on alkaline urea electrophoresis. Chicken cardiac TM likewise gave one band and it contains 4 SH/mole. In contrast pig, sheep and human cardiac TM contain respectively 2.6, 2.4, and 2.4 SH/mole and were resolved into two bands and on the different electrophoresis systems used, with a : ratio respectively of I:4.2, I:4.6, I:4.8. The -TM components from sheep skeletal and pig and sheep cardiac muscles were more positively charged than the rabbit skeletal -TM component, as shown in alkaline urea electrophoresis system. The and combinations of dimers found for skeletal muscle by other authors, were also found for cardiac pig TM.All the TM have the same effect on the Ca²⁺-stimulated ATPase activity of desensitized actomyosin (DAM) and on the Mg²⁺-stimulated ATPase activity of DAM with troponin-complex.This work suggests that the subunits of the TM from skeletal and cardiac muscles are heterogenous in their M.W. and their charges and that in the heart as well as in skeletal muscle a relationship seems to exist between the amount of the component and the speed of contraction of the muscle: a higher amount of this component was found in the bulky hearts which are also those which contract slower.