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The transition of Synechocystis PCC 6803 phytochrome Cph1 and its N-terrminal sensor domain from Pr to Pfr leads to net proton release, which is a function of proton release from decay of an intermediate and of proton uptake associated with Pfr formation. Protons arise from ionizable amino acid side chains.

Raman spectroscopy and nanosecond flash photolysis were used to study a recombinant phytochrome of the cyanobacterium Synechocystis. The findings indicate a resemblance between recombinant Synechocystis phytochrome and plant phytochrome with regard to Raman and visible spectral properties of the Pr and Pfr states. However, although the Synechocystis phytochrome undergoes a photoreversible conversion, red-shifted intermediates with kinetics different from those determined for the phytochrome intermediates were observed.

A study on the 59 kDa N-terminal module of the cyanobacterial phytochrome (Cph 1) from Synechocystis sp. PCC 680 in thermally stable forms using solution-state NMR spectroscopy is presented. A simple approach is established for preparing labeled phycocyanobilin (PCB) based on BG11 medium supplemented with an appropriate buffer and NAH(super 13)CO3 and Na(super 15) NO3 as sole carbon and nitrogen sources, respectively.

Results reveal that the carboxy terminal domain of phytochrome Cph1 mediates intersubunit trans-phosphorylation and signal transduction, suggesting its major role in the dimerization of Cph1 from synechocystis. Inersubunit energy transfer in the Cph1 dimer is looked at with the phycoerythrobilin/phycoerythrobilin homodimers and the hetero energy transfer using mixed phycoerythrobilin/phycocyanobilin heterodimers.