653 



N. E. Tolbert 



cells by filtration. This anomaly almost forces us to speculate 

 that part of the glycolate produced by photosynthesis is not free- 

 ly excreted, but that it is in or on the Chlorella in a position 

 vAiere it can be removed during filtration. In Mn deficient cells 

 glycolate excretion does not occur (28), presumably because gly- 

 colate is all converted to glycine and serine. 



By chloroplasts ; When chloroplasts are killed rapidly about 

 5 to 10% of the total C^^ fixed in 10 or 30 minutes is present as 

 products of the glycolate pathway and the remainder are sugar 

 phosphates. However, when the chloroplasts are filtered and 

 washed with saline solution on the 1 cm celite pad for 30 to 90 

 seconds in order to separate them from the supernatant medium, 50 

 to 707o of the total fixed C-"^"^ was found in the supernatant medium 

 as phosphoglycolate and glycolate, and the sugar phosphates had 

 nearly disappeared (15, 16). The sugar phosphate esters were not 

 themselves lost from the chloroplasts, but during filtration they 

 were converted to phosphoglycolate and excreted as such. For some 

 reason the filtration seems to have upset an equilibrium to create 

 this change. During C-'^'*02 by chloroplasts addition of a-hydroxy- 

 sulfonates also increases the amount of glycolate-C ^"^ , as if gly- 

 colate metabolism normally occurs in the chloroplasts even though 

 it does not accumulate (22). Again when glycolate-C^** was added 

 to chloroplasts it was not rapidly taken up nor metabolized. 



These chloroplast experiments prove that the system for phos- 

 phoglycolate synthesis resides in the chloroplasts. In addition 

 they indicate that a route for glycolate synthesis is from the 

 sugar phosphates of the carbon cycle and not by a C^ plus C^ con- 

 densation. The production of phosphoglycolate indicates that it 

 is the precursor of glycolate. 



Some free glycerate is excreted by spinach chloroplast but it 

 generally accounts for only a small part of the C-'^'* (15). The 

 conditions responsible for glycerate loss by the chloroplasts are 

 not as reproducible as those for glycolate excretion. It must be 

 emphasized, though, that free glycerate is excreted from the 

 chloroplasts, while phosphoglycerate is the major product inside 

 the chloroplasts. Phosphoglycolate phosphatase will not hydrolyze 

 phosphoglycerate, but perhaps there is some other phosphatase 

 within the chloroplasts which is responsible for phosphoglycerate 

 hydrolysis and excretion. 



Enzymes of the Glycolate Pathway 



Phosphoglycolate phosphatase is apparently specific for this 

 phosphate ester (13). It is ubiquitous in the green parts of 

 plants, for it is not in roots or etiolated leaves (Y. Yu, N. E. 



