658 



N. E. Tolbert 



Table 5. Effect of phosphate on C^'^Oa fixation by Chlamydomonas .-^i- 



No phosphate .001 M phosphate 



■'^Although fixation was much less without phosphate exact compari- 

 son between the experiments cannot be made because they were run 

 at different times. 



S 



of glycolate after 10 to 20 minutes. Addition of phosphoglycolate 

 to the algal medium is even more inhibitory to the rate of C'-'* I 

 labeling of glycolate than orthophosphate, although it substitutes 

 completely for orthophosphate in stimulating total CO2 fixation. 

 The great need for orthophosphate during C^^02 fixation by iso- 

 lated chloroplasts (40) can be replaced by equi-molar amounts of 

 phosphoglycolate. However, phosphoglycolate phosphatase activity 

 of the chloroplasts is not sufficient to have hydrolyzed much of 

 the phosphoglycolate to orthophosphate during the course of the 

 experiment. 



Manganese : Tanner et al. (17) claimed that Mn deficient Chlor- 

 ella do not produce glycolate. However, their data show that with 

 Mn deficient cells, which did not produce glycolate, 13.0% of the 

 C-'-'* fixed in 1 hr. was present as glycine and serine while with 

 normal cultures 9.4% of the C^"* was present as glycolate, glycine 

 and serine. Thus if one considers all the products of the gly- 

 colate pathway, Mn deficiency did not inhibit their synthesis, 

 but instead altered glycolate accumulation. A similar effect was 

 obtained by blue light. Mn"*"*" will serve as cofactor for glycolate 

 phosphatase but so will Mg"^"*". 



Recapitulation 



Glycolate synthesis during photosynthesis requires low CO2 

 concentration (less than 0.4%), high O2 concentration (20%) and 

 high light intensity. The phenomenon of a specific loss, or 

 movement or excretion of phosphoglycolate and glycolate by algae 

 or by chloroplasts remains unresolved. Glycolate excretion occurs 

 most rapidly with young algae cultures in the absence of phosphate 

 buffer. Manganese deficient cultures do not excrete glycolate. 

 Much of the fixed CO2 of photosynthesis pass through the glycolate 

 pathway which appears to be a metabolic sequal from the path of 

 carbon. Plant enzymes are known for each step of this pathway and 



