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Articles

Partial Characterization of Oat and Rye Phytochrome ¹

^a The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138

Purified oat and rye phytochrome were examined by analytical gel chromatography, polyacrylamide gel electrophoresis, N-terminal, and amino acid analysis. Purified oat phytochrome had a partition coefficient on Sephadex G-200 (₂₀₀) of 0.350 with an estimated molecular weight of 62,000; sodium dodecyl sulfate polyacrylamide electrophoresis gave an equivalent weight estimate. Purified rye phytochrome had a ₂₀₀ value of 0.085 with an estimated molecular weight of 375,000; sodium dodecyl sulfate electrophoresis gave a weight estimate of 120,000, indicating a multimer structure for the nondenatured protein. Comparative sodium dodecyl sulfate electrophoresis with purified phycocyanin and allophycocyanin gave a molecular weight estimate of 15,000 for allophycocyanin, and two constituent classes of subunits for phycocyanin with molecular weights of 17,000 and 15,000. Amino acid analysis of oat phytochrome confirmed a previous report; amino acid analysis of rye phytochrome differs markedly from a previous report. Oat phytochome has four detectable N-terminal residues (glutamic acid, serine, lysine, and leucine, or isoleucine); rye phytochrome has two detectable groups (aspartic and glutamic acids). Model experiments subjecting purified rye phytochrome to proteinolysis generate a product with the characteristic spectral and weight properties of oat phytochrome, as it has been described in the literature. It is concluded that the structural characteristics of purified rye phytochrome are likely those of the native protein.

¹ This research was supported by National Science Foundation Grant GB-15572, a grant from E. I. du Pont de Nemours and Company to WRB, and a National Science Foundation Predoctoral Fellowship to HVR.