Energy Transfer from NADPH to Protochlorophyllide in Isolated Protochlorophyllide Holochrome as Determined by UV-Fluorescence Excitation Spectroscopy at 77 K

The low -tem perature fluorescence excitation analysis o f different pro tochlorophyllide (PChlide) form s has been extended to the UV part o f the spectrum . A new band at abou t 360 nm was detected in excitation spectra o f active PChlide forms bound to isolated p ro to ­ chlorophyllide holochrom e. This band is very similar to the absorbance o f N A D P H in this region and its intensity depends on the redox state o f the surrounding medium . On illum ina­ tion at low tem perature the intensity o f the band decreases considerably w ithout any co rre­ sponding changes in the redox state o f “ free” N A D PH in the surrounding m edium . A new interm ediate state exhibiting a mixed excitation spectrum between PChlide and chlorophyllide (Chlide) was detected in the course o f PChlide photoconversion.