447 



Norman I. Bishop and H. Gaffron 



not remain constant during a subsequent dark period, but rather 

 diminish on account of the oxy-hydrogen reaction which ought to 

 occur within adapted cells, i.e., an active hydrogenase would be 

 present. Fig. h sums up the results of three experiments which 

 agree fully with the assumption of a simultaneous appearance of 

 the components of water. The curves indicate three ways by which 

 oxygen disappears after it has been evolved. The shape of the up- 

 per curve indicates an oxyhydrogen reaction inside the cells them- 

 selves. This reaction starts very soon after the beginning of 

 illumination and therefore forms a continuous part of the gas ex- 

 change in all three experiments during the entire period of obser- 

 vation. The middle curve represents readings obtained from a 

 reaction vessel with al kal i ne-pyrogal lol in the side arm. Here 

 the greater part of the oxygen evolved should be removed separate- 

 ly, leaving hydrogen behind. The lower curve represents the same 

 experiment but with a palladium catalyst in the center wel 1 '^ '. 

 Because of the immediate reformation of water there should be no 

 measurable gas exchange at all. This is approximately true after 

 the first ten minutes of illumination. There are two possible 

 reactions which may be responsible for the appearance of the 

 "extra" hydrogen observed in this experiment. First, excess hy- 

 drogen could be produced via a photochemical decomposition of an 

 endogenous hydrogen donor, as it occurs in purple bacteria. 

 Equally probable would be the oxidation of the internal hydrogen 

 donor by oxygen or its inrnediate precursor. The end result, in 

 either case, would be a shift in the hydrogen-oxygen stoichiomet- 

 ry in favor of the latter. 



COMPARISON OF EMERSON ENHANCEMENT EFFECTS IN PHOTOSYNTHESIS . 

 PHOTOREDUCTION . AND PHOTOHYDRQGEN PROQL'CTION 



Following the initial experiments of Emerson and coworkers on 

 the effect of the simultaneous addition of two selected wave- 

 lengths of light on the quantum yield of photosynthesis, it was 

 v;idely believed that the Emerson "enhancement" phenomenon would 

 be absent in photosynthetic systems in v-;h i ch oxygen is not pro- 

 duced, i.e., in bacterial photosynthesis and in photoreducti on. 

 Only recently have the experiments been performed wherein this 

 "deduction" has been conf i rmed(l 3. I^) , 



To explore further the hypothesis that the mechanism of hydro- 

 gen and oxygen evolution at least share steps in common, adapted 

 suspensions of Scenedesmus were irradiated with two wavelengths 

 of light, either singly or combined, which produced an enhancement 

 effect in photosynthesis. Under such conditions an approximately 

 equal enhancement of photohydrogen activity was observed. To the 



