Biophys J, September 2000, p. 1554-1560, Vol. 79, No. 3

Competition-Integration of Blue and Orange Stimuli in Halobacterium salinarum Cannot Occur Solely in SRI Photoreceptor

Giovanni Cercignani,^* Andrea Frediani, Sabina Lucia, and Donatella Petracchi

 ^*Università di Pisa, Dipartimento Fisiologia e Biochimica , I-56126 Pisa, and  Istituto di Biofisica del CNR, I-56127 Pisa, Italy

Experiments on the integration of blue and orange stimuli in Halobacterium salinarum were performed by using different combinations of blue and orange steps. The results show that the prevalence of the blue stimulus over the orange one depends on both the blue and the orange light intensities. A quantitative analysis of the current hypotheses on the phototransduction of orange and UV-blue light stimuli is presented, showing that the balancing between the two antagonistic stimuli should depend only on the intensity of the blue stimulus and not on that of the orange one, provided that the combination of the two stimuli occurs linearly at the photoreceptor stage. We conclude that blue and orange stimuli elicit distinct intracellular signals whose integration occurs downstream of the photoreceptor.

Biophys J, September 2000, p. 1554-1560, Vol. 79, No. 3
© 2000 by the Biophysical Society   0006-3495/00/09/1554/07  $2.00

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