L.K.M. Duysens 



(Qualitative evidence suggests a hydrogen transport scheme 

 with two different photochemical reactions in series. If the 

 two pigment systems have different pigment compositions, in ab- 

 sence of interaction two different action spectra for the va- 

 rious reactions are found under the appropriate conditions. We 

 feel that quantitative data, such as quantum efficiences and ac- 

 tion spectra for the various reactions, are very useful per- 

 haps necessary criteria to establish whether a hydrogen trans- 

 port scheme may be correct. 



RESULTS AlID IKTERPRETATION 



For the sake of brevity the results will not be discussed in 

 a historical and inductive sequence, but rather in a logical 

 and deductive one. The mechanism of hydrogen or electron trans- 

 port in algae or higher plants is discussed at the hand of the 

 scheme shown in Fig. 1. 



The arrows point into the direction of hydrogen transport. Of 

 the two components of the redox couples, only the component pre- 

 ponderant in darkness is represented. Cytochrome C 420 occurs 

 in darkness in the reduced form. The approximate B* values of 

 the redox couples are indicated at the left side: tne more 

 strongly reduciiig redox couples occur at the top of the drawing. 

 The two heavy upward pointing arrows indicate the two primary 

 photochemical reactions, 2 and 1, symbolized by the light quan- 

 ta hv2 and hv-^. Most other arrows point downward* which indica- 

 tes that the reactions occur spontaneously with a loss of free 

 energy. Such reactions may be "coupled" to a reaction in which 

 a gain of free energy occurs: the phosphorylation of ADP. The 

 two primary photochemical reactions, photoreactions 1 and 2, 

 &xe driven by two distinct pigment systems with different ab- 

 sorption and action spectra. Action spectra of these systems are 

 shown for two species as inserts in the scheme. The action spec- 

 trum of pigment system 1 in the red alga Porphyridium cruentun 

 shows that for photoreaction 1 quanta incident at 680, 



which are mainly absorbed by chlorophyll a, are about equal- 

 ly effective as quanta absorbed at 56O mfi mainly by the "acces- 

 sory pigment" phycoerythrin . The spectrum of system 2 shows 

 that quanta incident at 56O mji, which are absorbed mainly by 

 the phycoerythrin of pigment system 2, are much more effective 

 in photoreaction 2 than quanta incident at 680 or 430 ofi, which 

 are absorbed by chlorophyll a^ . Comparison of the action spectra 

 of the two systems shows that light absorbed by Porphyridium 

 at 680 and 43O m^ is more effective in exciting pigment system 

 1 than system 2, and that light absorbed at 56O a*i is more ef- 



