Ultraviolet Action Spectra of Positive and Negative Phototaxis in Platymonas subcordiformis.

The action spectra of positive and negative phototaxis in Platymonas show that the same photoreceptive pigment is involved in these two reaction types. In the far ultraviolet the algae are extremely sensitive to 220 mμ radiation. A minimum is observed at 255 mμ and a maximum at 275 mμ. This part of the action spectrum curve corresponds to the absorption spectrum of a protein which contains aromatic amino acids. In the near ultraviolet maximum occurred at 335 mμ, and in the visible region a small maximum at 405, a shoulder at 450, and a more prominent maximum at 495 mμ. The action spectrum curves in the near ultraviolet and the visible region correspond closely to the absorption characteristics of certain carotenoids. It is concluded that a carotenoprotein is the photoreceptive pigment complex in photic orientation. [ABSTRACT FROM AUTHOR]