In C
4 plants phosphoenolpyruvate (PEP) of the C
4 cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C
3 plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O
2 evolution by C
4 (
Digitaria sanquinalisL. Scop.) and C
3 (
Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C
4 mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (K
i = 2.1 mM) of 3-PGA dependentO
2 evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (K
t= 8.6 mM) of O
2 evolution in the C
4 mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO
2 evolution in the C
3 chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O
22 evolutionin both chloroplast types. The selectivity in inhibition ofO
2 evolution with 3-PGA as substrate suggests that the C
4 mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C
4 mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C
4 mesophyll chloroplasts.
1 Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987)
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