THE ENERGETICS OF PHOTOSYNTHESIS 



plex-bound heavy metals. Phenanthroline (1/35000 N) at pH 5 inhibits 

 photosynthesis of Chlorella to about 33%. The remaining 67% photo- 

 synthesis reacts to blue-green light, as in the absence of phenanthroline. It 

 must therefore be concluded that a heavy metal which is loosely bound or is 

 in the state of free ions must be present, in addition to a complex-bound heavy 

 metal. The former reacts with phenanthroline and the latter with HCN. 

 The identity of the second metal has not yet been established, but there is some 

 evidence that it may be vanadium. 



Warburg (40) observed that m-phenanthroline practically does not react 

 with heavy metal complexes. It is about 200 times less active than o- 

 phenanthroline. Thus, phenanthroline does not act as a narcotic but un- 

 doubtedly influences heavy metal catalysis. 



§ 32 The Significance of Vanadium 



The investigations of Bertrand (5) have shown that vanadium is found 

 throughout the whole vegetable kingdom. In the animal kingdom it is 

 rarely found; the blood cells of the tunicates contain vanadium instead of 

 iron. Arnon (2) established that vanadium is indispensable to the growth 

 of certain algae. It seems that the element has a specific action and that it 

 cannot be replaced by other heavy metals. Arnon divides the trace elements 

 into two groups. Group A contains iron, boron, manganese, zinc, copper 

 and molybdenum. Group B comprises cobalt, nickel, chromium, tungsten 

 and vanadium. The stock solution of group A has the following composition : 

 500 mg FeS04.7H,0 + 1000 mg Fe(N03)3'^H,,0 + 300 mg HBO3 + 200 

 mg MnS04.4HoO + 22 mg ZnS04.7H20 + 8 mg CUSO4.5H0O + 2 mg 

 (NH4)eMo70o4 + 1000 ml 0.005 N H2SO4. Two ml of this stock solution 

 are added to 250 ml of the culture salt solution (see § 15). It appears that 

 of group B only vanadium is necessary for Chlorella cultures. Warburg et al. 

 (54, 57) pointed out that the valency of vanadium is of importance. The 

 blue vanadylsulfate (VOS04.2H.,0) with tetravalent vanadium is inactive, 

 whereas pentavalent vanadium of the yellow sodium metavanadate (NaVOs. 

 4H2O) is very active. 



Growth with and without vanadium is identical during cultivation at high 

 light intensities. At low light intensities, as used in measuring the quantum 

 requirement (e.g., 50 ^A quanta/min, wave-length 5460 A), considerable 

 differences have been found. Table 15 shows the results of two experiments. 



TABLE 15 



The influence of vanadium, i = 54.3 jul quanta/min; 5460 A. Blue-green light: i = 0.6 ^1 



quanta/min. Time: 30~60 min. Addition of vanadium: 100 /xg /I. 



