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J. Biochem, 1988, Vol. 103, No. 2 218-224
© 1988 Japanese Biochemical Society

research-article

Conformational Changes of Alpha-Macroglobulin and Ovomacro-globulin from the Green Turtle (Chelonia mydas japonica)1

Atsushi Ikai, Faculty of Science, Toshiya Osada, Faculty of Science and Masaaki Nishigai, Faculty of Science

Department of Biophysics and Biochemistry, The University of Tokyo Bunkyo-ku, Tokyo 113

Green turtle plasma {alpha}-macroglobulin and ovomacroglobulin underwent conformational changes when they were treated with proteinases or methylamine. Their conformational changes were studied by HPLC gel chromatography, circular dichroism, and electron microscopy. The Stokes radii of native green turtle a-macroglobulin and ovomacroglobulin were estimated to be 84.3±0.5 Ä, and 93.0±0.5 Ä, respectively, by means of an HPLC experiment. After reaction with methylamine or proteinases, the Stokes radius of a-macroglobulin changed to 83.0±0.5 Ä or 85.4±0.5 Ä, respectively, and that of ovomacroglobulin to 93.0±0.5 Ä or 87.1+0.5 Ä. The circular dichroic spectra of native {alpha}-macroglobulin and ovomacroglobulin exhibited a negative band at around 215 nm, indicating the presence of ß-structure. Reaction of the two macroglobulins with methylamine resulted in a slight decrease in the ellipticity and reaction with proteinases led to a slight increase. The electron micrographic images of native {alpha}-macroglobulin and ovomacroglobulin can be described as deformed rings for the former and rugby balls for the latter. A common characteristic feature of the two molecules was that the central parts of the molecules were only thinly occupied by subunit. After reaction of macroglobulins with proteinases, the void spaces became partially filled and their overall shape more rectangular. Methylamine treatment caused a structural change only in {alpha}-macroglobulin but not in ovomacroglobulin. The difference in the susceptibility of the macroglobulins to methylamine was taken as an indication of evolutional divergence of the two homologous proteins within the last 300 million years.

1 This work was supported by a Grant-in-Aid for Scientific Research (No. 62220009) from the Minitry of Education, Science and Culture of Japan.


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