3-Phospho-glycerate

O -. - which is isomerized by transfer of the phosphoryl group to give 3-phospho-glycerate. 

All vertebrates can form certain amino acids from amphibolic intermediates or from other dietary amino acids. The intermediates and the amino acids to which they give rise are a-ketoglutarate (Gin, Gin, Pro, Hyp), oxaloacetate (Asp, Asn) and 3-phospho-glycerate (Ser, Gly). 

After donating its phosphate group to ADP, 1,3-diphosphoglycerate is converted into 3-phospho-glycerate. This reaction is followed by enzymic modification to 2-phosphoglycerate. 

Huskins, K.R. Bernhard, S.A. Dahlquist, F.W. Halibut muscle 3-phospho-glycerate kinase. Chemical and physical properties of the enzyme and its substrate complexes. Biochemistry, 21, 4180-4188 (1982)... 

The product of this metabolic sequence, pyruvate, is a metabolite of caitral importance. Its fate depends upon the conditions within a cell and upon the type of cell. When oxygen is plentiful pyruvate is usually converted to acetyl-coenzyme A, but under anaerobic conditions it may be reduced by NADH + H+ to the alcohol lactic acid (Fig. 10-3, step h). This reduction exactly balances the previous oxidation step, that is, the oxidation of glycer-aldehyde 3-phosphate to 3-phospho-glycerate (steps a and b). With a balanced sequence of an oxidation reaction, followed by a reduction reaction, glucose can be converted to lactate in the absence of oxygen, a fermentation process. The lactic acid fermentation occurs not only in certain bacteria but also in our own muscles under conditions of extremely vigorous exercise. It also occurs continuously in some tissues, e.g., the transparent lens and cornea of the eye. 

The subsequent transfer of the 1-phospho group to ADP is an important energy-yielding step in metabolism (Chapter 12). When arsenate substitutes for phosphate the acyl arsenate (l-arseno-3-phospho-glycerate) is hydrolyzed to 3-phosphoglycerate. 

The overall effect is to transport C02 from the mesophyll cells into the bundle sheath cells along with two reducing equivalents, which appear as NADPH following the action of the malic enzyme. The C02, the NADPH, and additional NADPH generated in the chloroplasts of the bundle sheath cells are then used in the Calvin-Benson cycle reactions to synthesize 3-phospho-glycerate and other materials. Of the C02 used in the bundle sheath cells, it is estimated that 85% comes via the C4 cycle and only 15% enters by direct diffusion. The advantage to the cell is a higher C02 tension, less competition with 02, and a marked reduction in photorespiration. 

Borchert, S., Grosse, H., and Heldt, H. W. 1989. Specific transport of inorganic phosphate, glucose 6-phosphate, dihydroxyacetone phosphate and 3-phospho-glycerate into amy-loplasts from pea roots. Fed. Eur. Biochem. Soc. 253,183-186. 

STEP 4 Iwmeriaation by transfer of u phosphate group yields 3-phospho glycerate. 

The anhydride phosphoryl group is easily transferred in another enzyme-catalyzed reaction, 1,3-diphosphoglycerate reacts with ADP to yield 3-phospho-glycerate and ATP. The 3-phospho ycerate goes on in the glycolysis process. 

Hydration and isomerization. Conjugate addition of water to the double bond of phosphoenolpyruvate takes place in a process similar to that of step 2 in the j3-oxidation pathway (Figure 29.2). Isomerization then occurs by transfer of a phosphate group from C2 to C3, 5helding 3-phospho-glycerate. 

FIGURE 13-4 Hydrolysis of 1,3-bisphosphoglycerate. The direct product of hydrolysis is 3-phospho-glyceric acid, with an undissociated carboxylic acid group, but dissociation occurs immediately. 

Glyceraldehyde 3-phosphate, an aldehyde, is oxidized to 3-phospho-glycerate, a carboxylic acid. 

As stated earlier, the rate-limiting step in the Calvin cycle is the carboxy-lation of ribulose 1,5-bisphosphate to form two molecules of 3-phospho-glycerate. The activity of rubisco increases markedly on illumination. The addition of CO2 to lysine 201 of rubisco to form the carbamate is essential for Mg coordination and, hence, catalytic activity (Section 20.1.1). Carbamate formation is favored by alkaline pH and high concentrations of Mg ion in the stroma, both of which are consequences of the light-driven pumping of protons from the stroma into the thylakoid space. Magnesium ion concentration rises because Mg ions from the thylakoid space are released into the stroma to compensate for the influx of protons. 

DAS have been determined for a number of proteins, with an emphasis on proteins which contain two tryptophan residues. In these cases one hopes that each tryptophan will display a single decay time, so that the I S represent the emission spectra of the individual residues. One example is provided by a study of yeast 3-phospho-glycerate kinase (3-FGK), which has two tryptophan residues. Rom a number of pH- and wavelengdi-dependent measurements, the 0.6-ns component in die decay was associated with one residue, and the 3.1- and 7.0-ns components were associated widi die second tryptophan residue. The wavelength-dependent intensity decays were... 

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