Scientia Sinica

No. 1 TSAO, TAN, & PENG: TROPOMYOSINS FROM DIFFERENT SOURCES 93

overnight. The partially dehydrated lumps were then chopped into a finer state and again soaked in a fresh change of ethanol. This was followed by another change of ethanol and two changes of ether, and the debris was allowed to dry in air. The dehydrated muscle was extracted with neutral M KCl or NaCl, and the subsequent steps followed closely those outlined by Sheng and Tsao", except that the salting-out range of the prawn tropomyosin was between 15 and 30% saturation of ammonium sulphate instead of 40-70% as for all the other tropomyosins so far investigated. The ammonium sulphate

paste thus prepared bears the appearance of a transparent gel.

All the above-mentioned tropomyosins were purified three or four times, and were electrophoretically homogeneous in a versonal buffer, pH 8.5, or a phosphate buffer, pH 6.5.

As the available amount of tropomyosins derived from the foot and adductor muscles of bivalves was much limited, we only carried out electrophoretic measurements and crystallization experiments with these proteins. Crystallization was effected by dialysis against 0.01M sodium acetate pH 5.4, containing 16 g of ammonium sulphate per litre following the method initiated by Bailey", Crystals of Anodonta foot muscle tropomyosin did not appear until after standing for a month in the ice-chest. The crystallization of prawn tropomyosin required a slightly higher ionic strength and a lower pH. An aqueous 2-3% solution of this tropomyosin was first dialyzed against 0.01 M sodium acetate, pH 5.8, containing 30 g of ammonium sulphate per litre. Overnight, 1 ml of M acetate buffer, pH 4.8, was added to each 100 ml of the dialysate. Crystals appeared in the course of one or two days. The various crystalline forms are given in plates I to IIL.

The samples of the bovine, the rat, the carp, the shell-varp, the crab, and the uterine tropomyosins used in electrophoretic experiments were those [38]

prepared by Sheng and Tsao™™. 3. Analysis of nitrogen content and protein concentration.

Purified samples were first dialysed against several changes of water, then - against 0.1 M KCl to remove ammonium sulphate, and finally against several more changes of water to remove the last traces of all salt ions. Aliquots were taken for the determination of the dry weight of protein and the nitrogen content. Dry weight was the constant weight obtained after freezedrying over P,Os. These data combined to give the total nitrogen content of each protein. The values for duck gizzard, pig heart, prawn and sepia tropomyosins were found to be respectively 15.5%, 15.0%, 17.7% and 19.0%. Bailey®" reported a value of 16.7% for rabbit tropomyosin.

Protein concentrations were determined by the micro-Kjeldahl method™, employing the total nitrogen values given above and expressed as g. protein 100 ml solution. Some samples were also analyzed with the aid of the Zeiss interferometer, the drum readings and concentrations for each protein having