Scientia Sinica

No. 1 TSAO, TAN, & PENG: TROPOMYOSINS FROM DIFFERENT SOURCES 107

of which myosin is composed and elaborated. Although this original proposal of Bailey®!! could not be substantiated by the depolymerization studies of Tsao), and the comparative studies of Robinson™! and of Sheng and Tsao®!, it has taken on a new form in the work of Kominz, Hough, Symond and Laki!! who, on the basis of amino acid analysis, suggested that both tropomyosin and actin were structural components of myosin. Ellenbogen and Olson’s finding and our own results indicate that in cardiac muscle systems, at any rate, molecules of myosin and tropomyosin may be of similar size. This fact alone seriously undermines the contention of Kominz et al), Further comparative studies are evidently needed to settle the important points of the biogenesis ef myosin and of the relationship of tropomyosin and myosin.

Cytological investigations, especially those carried out recently with the electron microscope, have thrown much light on the fine structures of the striated muscle. There are as yet no convincing indications as to how the

various structural components—actin, myosin, tropomyosin, etc—are linked |

together in.the A and I bands and what exactly are the molecular events when the bands undergo changes during muscle contraction. From a comparative point of view, the anatomically much simpler smooth muscle might be a more suitable material for biochemical investigation. In this respect, existing datal!? 11» 13,225,2°7] appear to be rather limited in scope; they are mainly concerned with the adenosinetriphosphatase activity and the behaviour of the ill-defined actomyosin system. The present study has been an attempt to cover only some aspects of the chemistry of tropomyosin. A comparative study of the size, shape, aggregation, mutual interaction and enzymic activities of other isolated, purified protein components of smooth muscle may prove to be of benefit to our understanding of the contractile mechanism of muscle.

V. SUMMARY

1. Five new members have been added to the family of tropomyosins prepared from sources other than rabbit skeletal muscle. These were ‘solated from the mantle of the sepia (Sepia esculenta), the body muscle of the prawn (Penaeus orientalis), the foot muscle of the bivalve (Anodonta pacifica) and the adductor muscles of the bivalves (Anodonta pacifica and Cristaria plicata). All have been crystallized.

2, The size, shape, polymerizability and electrophoretic behaviour of

tropomyosins of duck gizzard and sepia mantle smooth muscles, and pig cardiac and prawn striated muscles have been determined and compared

with those of rabbit tropomyosin. 3, The polymerizability of duck gizzard tropomyosin is higher than that of either pig heart or rabbit muscle tropomyosin.