Modification of Mitosis by Chemicals

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Abstract
Actomyosin was prepd. by a method slightly modified from that of Greenstein and Edsall (1940). Light-scattering measurements were made with an apparatus employing the 546 millimicron line of a mercury vapor lamp as a light source and a photomultiplier for registering intensities of scattered light. Intensities were detd. for light scattered in the horizontal plane at 45[degree] and 135[degree] with light transmitted through 1% actomyosin in 0.5 [image] KCl and 0.09 [image] KH2PO4-K,HPO4 buffer at pH 6.8. An avg. value of 3.4 was obtained for the ratio of the forward to backward scattering at the angles mentioned. The value indicates that the actomyosin particles in 0.5 [image] KC1 at pH 6.8 are slightly coiled. The ratio increased to 4.7 after adding ATP to make its final concn. 1% in a soln. of actomyosin in 0.5[image] KC1 and buffer at pH 6.8. The increase in ratio is consistent with an increase in coiling of the actomyosin. No change in pH of the actomyosin soln. occurred after adding ATP. Tenfold dilution of the ATP-actomyosin soln. with 0.5 [image] KC1 did not change the ratio of 4.7, and there was no change in light transmission after adding ATP. This indicates that the change in ratio is not the result of aggregation or coagulation of the actomyosin. Addition of KC1 to actomyosin soln. over a range of 0.5 to 2 [image] KC1 did not alter the ratio at the previously stated angles. This indicates that actomyosin does not dissociate at higher concns. of KC1. It indicates no change in size or shape of the protein. Samples of untreated actomyosin were prepd. by placing a drop of 0.01% actomyosin soln. in 0.5 [image] KC1 on a collodion film supported by a copper screen. The sample was dried, washed with dist. water, and was gold shadow-cast by the method of Williams and Wyckoff (1944). The electron micrograph showed the typical entangled, fibrillar structure of actomyosin. Samples were then prepared from solns. of 0,01% actomyosin in 0,5 [image] KC1 to which ATP was added to make its final concn. 0.01%. Most of the elongated fibrils of actomyosin were changed into short, thick, irregular forms. ATP increases the degree of coiling of actomyosin.

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