Abstract
Abstract A pigment protein which undergoes a reversible light-induced absorbance change was purified about 2000-fold from cells of the phototactic cellular slime mold, Dictyostelium discoideum. The photoresponsive pigment was solubilized by sonication of the mitochondrial fraction, and purified by ammonium sulfate precipitation and centrifugation in sucrose gradients. The absorption spectrum of the photoresponsive pigment, which shows a strong band at 430 nm and two broad low extinction bands in the 550- to 590-nm region, is consistent with the action spectrum of phototaxis. Thus, this pigment appears to be the photoreceptor pigment for phototaxis in pseudoplasmodia of D. discoideum.
Highlights
The pseudoplasmodia can migrate over the substratum covering more than 20 mm in a day
The action spectrum of this response shows two broad peaks, one in the 400. to 450.nm region and one in the 550- to 600-nm region [1, 2]. This action spectrum clearly distinguishes the phototasis of D. discoideum from the typical “blue light responses” such as phototropism of Phycomyces which show no response to wavelengths longer than 520 nm [3]
The action spectrum for the induction of the absorbance change extends out to 600 nm, and is difficult to reconcile with the absorption spectrum of these cytochromes
Summary
A pigment protein which undergoes a reversible lightinduced absorbance change was purified about 2000-fold from cells of the phototactic cellular slime mold, Dicfyostelium discoideum. The absorption spectrum of the photoresponsive pigment, which shows a strong band at 430 nm and two broad low extinction bands in the 550- to 590-nm region, is consistent with the action spectrum of phototaxis. This pigment appears to be the photoreceptor pigment for phototaxis in pseudoplasmodia of D. discoideum. The action spectrum for this light-induced absorbauce change is consistent with the action spectrum for phototactic migration by the pseudoplasmodia [2]. Extract using the light-induced absorbance change as an assay for activity of the pigment
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