3-Phosphoglycerate transport

Glycine is then transported to the mitochondrial matrix where the conversion of two glycines to one serine occurs with the loss of CO2 and NH3 from the pool of fixed molecules. The serine is transported into the peroxisome, where it is deaminated to glycerate. The glycer-ate is transported back to the chloroplast, where it is phosphorylated to 3-phosphoglycerate for the Calvin-Benson cycle. 

Starch and sucrose, key substrates for the development of dental caries, are exclusively synthesized by plants. They are made in plant leaves by a process called photosynthesis, which utilizes sunlight as the energy source. This chapter outlines the light and dark reactions of photosynthesis and compares the light reaction with mitochondrial electron transport (Sect. 1). The key dark reaction, the production of phosphoglycerate by the enzyme ribulose bisphosphate carboxylase (rubisco), is described along with the production of fructose, sucrose, and starch (Sect. 2). The chapter concludes with a detailed discussion of the roles of starch and sucrose in plant metabolism (Sect. 3). 

Fig.2.10 Phosphoglycerate utilization, (a) During the day. Photosynthesis in the chloroplast makes starch until there is no more room. The Calvin cycle continues to make triose phosphate, which exits the chloroplast in exchange for organic phosphate (Pi) entering the chloroplast and converting ADP to ATP. In the cytosol, the triose phosphate is mostly converted to sucrose but also to small amounts of other compounds such as amino acids for transport throughout the plant, (b) During the night. Phosphorylase is activated and it breaks up the starch to glucose 6-phosphate from which triose phosphate is made. The triose phosphate is exchanged for Pi. The Pi is a substrate for phosphorylase and keeps it active. Once in the cytosol, the triose phosphate is transferred mostly to mitochondria for respiration...

A second mechanism of protection from caries is the incorporation of fluoride into bacterial biofilms where it inhibits enolase. Enolase catalyzes the production of phospho-enolpyruvate, the precursor of lactate in glycolysis, from 2-phosphoglycerate during glycolysis (Fig. 16.7 - see also Fig. 1.7). In addition, oral bacterial uptake of mono- and disaccharides mostly utilizes the phosphoenolpyruvate transport system to transfer them into the cytosol (Sect. 15.2.2). Fluoride therefore inhibits not only lactic acid production, but also the phosphoenolpyruvate transport system-mediated uptake of saccharide substrates. In short, fluoride inhibits saccharolytic fermentation by many oral bacteria. 

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