Scientia Sinica

A COMPARATIVE, PHYSICO-CHEMICAL STUDY OF TROPOMYOSINS FROM DIFFERENT SOURCES*

Tsao T1en-Cuin (SARS), Tan PerHsine (#@(mlS2), and Penc Cu1a-Mu (GRE)

(Institute of Physiology and Biochemistry, Academia Sinica)

I. INTRODUCTION

Our knowledge of and speculations on the possible structure and function of tropomyosin have been based, as in the case of actin and myosin, chiefly on the investigations of the rabbit or the frog skeletal muscle. Recently an increasing number of reports have appeared!'*!, which drew attention to the contractile apparatus of the smooth and the cardiac muscles as well as the striated muscle of animals other than the rabbit or the frog. Considerations were also given to the changes of protein components of muscle during drastic physiological or pathological changes such as embryonic development, enlargement of uterus during pregnancy, atrophy and dystrophy, metamorphosis, etc. These studies concerned mainly the activity of adenosine triphosphatase, the contents and properties of actin, myosin and adenosine triphosphate and the interaction of the three. They serve to establish the essential similarity of the contractile apparatus in muscles from different sources, and at the same time reveal a number of significant variations, both in quantity and quality, in their enzymic or structural make-up. These differences, no less than the similarities, should naturally be borne in mind in any attempt at the elucidation of the contractile mechanism of muscle.

There is at present no definite clue to the physiological function of another structural protein, tropomyosin. Is it the substrate for the contractile or holding function of muscle, or does it play yet other roles in muscle physiology? The structure and the physico-chemical properties of rabbit skeletal tropomyosin were already the subjects of extensive investigations and the size, shape and aggregation of this molecule'™’, its amino acid composition®” *! and its terminal structure! ° are now fairly well known. With regard to tropomyosins from other sources, Bailey! prepared tropomyosins from whiting, and horse and pig hearts; Hamoir! *! investigated the ultracentrifugal and

First published in Chinese in Acta Physiologica Sinica, Vol. X1X, Nos. 3-4, pp. 389—+06, 1955.