Partial characterization of the interaction between phytochrome and a particulate fraction of maize coleoptiles

Extraction of red light-irradiated maize coleoptiles with Mg⁺⁺-containingbuffers enhances the pelletability of phytochrome. The enhancedphytochrome pelletability is taken to represent in vivo interactionof phytochrome with its binding site. The bonds involved inthe interaction appear to be ionic. This is shown by the requirementof Mg⁺⁺ for the enhanced pelletability and for the maintenanceof phytochrome repelletability during subsequent fractionation.Also, the phytochrome-binding site complex is responsive tothe disruptive effect of high ionic strength buffers, but itisrelatively insensitive to pH changes. Due to the ionic natureof the interaction, the complex can withstand membrane dissolutionby the non-ionic detergent Triton X 100. Though the molecularbasis for the persistent re-pelletability of phytochrome afterdetergent treatment remains to be determined, data obtainedindicate that the phenomenon is not due to denaturation of thephytochrome molecule per se. (Received May 25, 1976; )