166 



PROBLEMS OF PHOTOSYNTHESIS 



lactic acid are added to a solution containing Chlorella extract and DPN+. 

 The light absorption at 3400 A increases only when D-lactic acid is added, 

 as only this isomer can be dehydrogenated to pyruvic acid by D-lactic acid 

 dehydrogenase. 



Fig. 62. The lactic acid dehydrogenase 

 of Chlorella and d- and L-lactic acid. 

 Curve I: L-( + )-lactic acid. Curve H: 

 D-( — )-lactic acid. Only curve H shows 

 light absorption at 3400 A indicating that 

 only D-lactic acid reduces DPN+ (War- 

 burg et al., Zschr. Naturf.). 



The X-cells exhibiting high lactic acid production are particularly useful 

 when the glutamic acid of Chlorella is to be decomposed without adding NaF. 

 Owing to lactic acid formation in these cells, glutamic acid is decomposed 

 anaerobically without NaF and aerobically resynthesized. 



§ 63 Breakdown and Resynthesis of Glutamic Acid 



Lyophilized cells of Chlorella cannot divide and cannot reduce CO2 upon 

 illumination. When suspended in water or in salt solutions, they are able 

 to decarboxylate L-glutamic acid but not other amino-acids or pyruvic acid. 

 They are thus particularly useful for determining glutamic acid. The side- 

 arm of a conical manometer vessel contains 20 mg lyophilized cells. The 

 vessel itself contains 3 ml of the glutamic acid solution to be analysed (pH 

 3.8). After tipping the contents of the side-arm into the vessel, the pH in- 

 creases to about 5. The temperature is 20 ° C and the gas phase contains 

 argon only. Figure 63 shows that after 280 min 4.49 jumole CO2 are pro- 

 duced by decarboxylation of the 4.8 Mmole glutamic acid added (curve II). 

 Curve I represents a control experiment without the addition of glutamic 

 acid. The CO2 of curve I originates from the glutamic acid present in the 

 lyophilized cells where it is so tightly bound that extraction is very difficult 

 even at 100° C. 



The breakdown and resynthesis of glutamic acid can also be demonstrated 

 by means of paper chromatography. Various concentrations of NaF are 

 added under anaerobic and aerobic conditions to a suspension of living Chlo- 

 rella (100 jul cells in 3 ml salt solution, pH 3.8, temperature 20 ° C). When the 



