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Articles

Purification of Oat and Rye Phytochrome ¹

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

A purification procedure employing normal chromatographic techniques is outlined for isolating phytochrome from etiolated oat (Avena sativa L.) seedlings. Yields in excess of 20% (25 milligrams or more) of phytochrome in crude extract were obtained from 10- to 15-kilograms lots. The purified oat phytochrome had an absorbance ratio (A₂₈₀ nm/A₆₆₅ nm) of 0.78 to 0.85, comparable to reported values, and gave a single major band with an estimated molecular weight of 62,000 on electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. A modification of the oat isolation procedure was used to isolate phytochrome from etiolated rye Secale cereale cv. Balbo) seedlings. During isolation rye phytochrome exhibited chromatographic profiles differing from oat phytochrome on diethylaminoethyl cellulose and on molecular sieve gels. It eluted at a higher salt concentration on diethylaminoethyl cellulose and nearer the void volume on molecular sieve gels. Yields of 5 to 10% (7.5-10 milligrams) of phytochrome in crude extract were obtained from 10- to 12-kilogram seedling lots. The purified rye phytochrome had an absorbance ratio of 1.25 to 1.37, significantly lower than values in the literature and gave a single major band with an estimated molecular weight of 120,000 on electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. It is suggested that the absorbance ratio and electrophoretic behavior of rye phytochrome are indices of purified native phytochrome, and that oat phytochrome as it has been described is an artifact which arises as a result of endogenous proteolysis during isolation. A rationale is provided for further modifications of the purification procedure to alleviate presumed protease contaminants.

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.