Recombinant phytochrome of the moss Ceratodon purpureus (CP2): fluorescence spectroscopy and photochemistry

The recombinant phytochrome of the moss Ceratodon purpureus (CP2) expressed in Saccharomyces cerevisiae and reconstituted with phycocyanobilin (PCB) w as investigated using fluorescence spectroscopy. The pigment had an emissio n maximum at 670 nm at low temperature (85 K) and at 667 nm at room tempera ture (RT) and an excitation maximum at 650-652 nm at 85 K (excitation spect ra could not be measured at RT). Both spectra had a half-band width of appr ox. 30-35 nm at 85 K. The fluorescence intensity revealed a steep temperatu re dependence with an activation energy of fluorescence decay (E-a) of 5.9- 6.4 and 12.6-14.7 kJ mol(-1) in the interval from 85 to 210 K and from 210 to 275 K, respectively. The photochemical properties of CP2/PCB were charac terised by the extent of the red-induced (lambda (a) = 639 nm) Pr conversio n into the first photoproduct lumi-R at 85 K (gamma (1)) of approximate to0 .07 and into Pfr at RT (gamma (2)) of approximate to0.7. From these charact eristics, CP2/PCB can be attributed to the Pr " photochemical type with gam ma (1) less than or equal to 0.05, which comprises the minor phyA fraction (phyA "), phyB, Adiantum phy1 and Synechocystis Cph1 in contrast to the maj or phyA' fraction (Pr' type with gamma (1) = 0.5). Within the Pr " type, it is closer to phyA " than to phyB and Cph1. (C) 2000 Elsevier Science S.A. All rights reserved.