Studies on plantacyanin. III. Structural data obtained by CD and MCD methods and antigenic properties of the protein
1988
Nersissian, A.M. | Nalbandyan, R.M.
Absorbance, CD and MCD spectra of plantacyanins from spinach leaves and cucumber peelings were compared, and the effects of high pH and the reduction and the removal of copper in these spectra were considered. Using the approach of Hennessey and Johnson (Hennessey, J.P., Jr. and Johnson, W.C., Jr. (1981) Biochemistry 20, 1085-1094) the secondary structure parameters of the proteins were determined. The secondary structure consists mainly of alpha- and 3(10)-helix, antiparallel beta-sheet and random structure, although different types of beta-turn also contribute to some extent. Secondary structure parameters were found to be sensitive to the redox state and the presence of copper as well as pH. Differences in the secondary structure of two plantacyanins were also noted. It was established that the copper of plantacyanins, besides having its characteristic bands in the visible spectrum also contributes to a certain extent to the UV spectrum at 250 nm and to the CD spectrum of the 'aromatic' region. These UV bands seem to belong to the copper-sulphur bond. MCD spectra reveal that the tryptophan content in cucumber plantacyanin was twice as high as in spinach plantacyanin. Antibodies to spinach and cucumber plantacyanin was twice as high as in spinach plantacyanin. Antobdies to spinach and cucumber plantacyanins were obtained, and it was shown that no cross-reactivity between spinach antibodies and cucumber protein, or spinach protein and cucumber antibodies occurs. The reduction or the removal of copper does not change the antigenic properties of plantacyanins.
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