2.3 bis-phosphoglycerate

Now for the glycerates. 1,3 bis-phosphoglycerate [compound (iii)] is the only molecule with two attached P groups. When we number the carbon atoms in an aliphatic organic compound we invariably start at the most oxidized carbon (drawn at the top of the chain), so carbon 2 of the glyceric acid derivatives must be the middle... 

G.M. Blackburn, D.L. Jakemean, A.J. Ivory, M.P. Williamson, Synthesis of phosphonate analogues of 1,3-bis-phosphoglyceric acid and their binding to yeast phosphoglycerate kinase, Bioorg. Med. Chem. Lett. 4 (1994) 2573-2578. 

Oxidation of Glyceraldehyde 3-Phosphate to 1,3-Bisphos-phoglycerate The first step in the payoff phase is the oxidation of glyceraldehyde 3-phosphate to 1,3-bis-phosphoglycerate, catalyzed by glyceraldehyde 3-phosphate dehydrogenase ... 

Fig. 1. The reductive pentose phosphate cycle (RPP). The solid lines indicate reactions of the RPP cycle. The number of lines per arrow indicates the number of times each reaction occurs for one complete turn of the cycle in which three molecules of COj are converted to one molecule of G3P. Each reaction of the cycle occurs at least once. The double dashed lines indicate the principal reactions removing intermediate compounds of the cycle for biosynthesis. Abbreviations RuBP, ribulose 1,5-bis-phosphate PGA, 3-phosphoglycerate DPGA, 1,3-diphosphoglycerate, FBP, fructose 1,6-bisphos-phate F6P, fructose 6-phosphate SBP, sedoheptulose 1,7-bisphosphate S7P, sedoheptulose 7-phosphate Xu5P, xylulose 5-phosphate R5P, ribose 5-phosphate Ru5P, ribulose 5-phosphate TPP, thiamine pyrophosphate. From Ref. 1.

Three of the reactions in the Calvin cycle are irreversible and serve to drive the whole cycle in a clockwise direction. The first step in the cycle can be regarded as the action of carbon dioxide on ribulose-l,5-diphosphate to produce two molecules of 3-phosphoglyceric acid which is then converted into 1,3-diphosphoglyceric acid by the action of ATP and the appropriate enzyme. The important first step is catalysed by the phosphoprotein D-ribulose-1,5 bis phosphate carboxylase oxygenase (RUBISCO) which is probably the most abundant enzyme in the world. 

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