Scientia Sinica

No. 1 TSAO, TAN, & PENG: TROPOMYOSINS FROM DIFFERENT SOURCES — 105

lying respectively near-11 X 10° and -9 * 10° cm?/V/sec. The slight fluctuation may be a reflection of the possible differences in chemical composition. It is conceivable that the nature and the relative abundance of polar and nonpolar side chains, the amount of amide nitrogen and of nonprotein constitutents may vary from one tropomyosin to another. The marked variation in the total nitrogen content described in section II-3 points to the same direction.

5. Crystallization of tropomyosin

Tropomyosins from rabbit and whiting striated muscles and pig cardiac muscle were crystallized by Bailey®"!. Hamoir!! effected the

crystallization of carp tropomyosin and nucleotropomyosin. Sheng and _

Tsao!) obtained crystalline tropomyosins and nucleotropomyosins from the skeletal muscles of bovine adult and foetus, rat, shell-carp, toad and crab and the smooth muscles of bovine uterus and duck gizzard. In the present investigation we added five new members to the family of crystalline tropornyosins. These were derived from sepia mantle, the body muscle of prawn, the foot muscle of the bivalve Anodonta and the adductor muscles of the bivalves Anodonta and Cristaria. In general, tropomyosin crystals appear to be of two kinds: those derived from the skeletal and the cardiac muscles of the adult or foetus of higher animals possess straight edges (flat plates—squares, parallelograms; six-edged spindles; solid structures) and those from the smooth muscles of higher animals and from the smooth and striated muscles of lower invertebrates are elongated smooth spindles. The presence of ribonucleic acid seems to influence only the thickness but not the overall shape of the crystals.

TV. Discussion

Our present and previous'*) investigations have demonstrated that in respect of the molecular size, shape, solubility, crystalline form, polymerizability, electrophoretic mobility and the amount of associated ribonucleic acid, tropomyosins derived from all types of muscle (striated, smooth and cardiac) taken from different animals of the phylogentic scale (mammalia, aves, reptilia, amphibia, pisces, arthropoda and mollusca) exhibit delicate or marked species and functional differences. The physiological réle of tropomyosin in muscle is as yet unknown. To differentiate tropomyosin from other structural proteins of muscle, it is necessary at this stage to forsake biological activity but to rely on physico-chemical characteristics. In view of the above-mentioned differences, some physico-chemical properties must necessarily be excluded or more stringently specified. As a class of protein, the salient characteristics of tropomyosins are: (1) the ability to polymerize in neutral solutions in the absence of salt and the reversible depolymerization by salt ions; (2) the ability to crystallize under favourable conditions; (3) the high asymmetry, with axial