Phosphoglycolic acid

Triosephosphate isomerase, for example, catalyzes the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate with fccat values that vary with pH, whereas is pH independent in the neutral range. This behavior appears consistent with mechanisms in which the enzyme combines with either monoanionic or dianionic forms of the substrate with similar affinity, but only the latter forms a productive complex, ES , which goes on to form products. Unlike an ordinary substrate analog, a transition-state analog for this reaction would be expected to be bound tightly only as a dianionic species, and this appears to be the case for the inhibitor 2-phosphoglycolic acid. ... 

Phosphoglucose isomerase, 381, 382 Phosphoglycerate, 388, 390 Phosphoglycolate, 388 2-Phosphoglycolic acid, 18 2-Phosphoglycolohydroxamate, 23, 25 Phosphonomycin, 543 Phosphoribosyl pyrophosphate amido-transferase, 420, 424... 

The structure DAHPS from E. coli with Mn " " and the substrate analogue, 2-phosphoglycolate (PGL), in the active site has been determined. Mn " ", the most efficient metal activator of DAHPS, is coordinated by four amino acid side chains the PGL and a water molecule complete the octahedral coordination (Figure 25). " This structure is notable for the fact that it contains a rare example of a Mn—S bond in a protein. The Mn—S bond is quite long, 2.74 A, and spectroscopic evidence for the formation of this bond is lacking. " ... 

Hydroxycyclopropanecarboxylic acid phosphate HCP 34 is an analogue of phosphoenolpyruvate (PEP) 35 which is metabolized by various enzymes. HCP 34 is a potent competitive inhibitor of enzymes utilizing PEP 35, such as PEP carboxylase, enolase, pyruvate kinase, and probably other enzymes. It is a substantially better inhibitor than phospholactate 36 or phosphoglycolate 37, presumably because of the similarity of its geometric and electronic structures with phosphoenol pyruvate,Eq. 12 [28]. 

The same active site of ribulose bisphosphate carboxylase also catalyzes a competing reaction in which 02 replaces C02 as a substrate. The products of this oxygenase reaction are 3-phosphoglycerate and a two-carbon acid, 2-phosphoglycolate (fig. 15.27). Phosphoglycolate is oxidized to C02 by 02 in additional reactions involving enzymes in the cytosol, mitochondria, and another organelle, the peroxisome. This photorespiration is not coupled to oxidative phosphorylation, and it appears to constitute a severe... 

Samples of column fractions (47.5 pi) were mixed with 2.5 pi of 10 mM CAIP or phosphoglycollate and incubated at room temperature. Reaction was stopped by the addition of 2.5 pi of trifluoroacetic acid. Precipitated protein was removed by centrifugation and the orthophosphate concentration in the supernatant liquid was measured. Disappearance of CAIP was measured in reaction mixtures of total volume 0, 1 ml containing 0. 9 nmol CAIP, 1 mM NADPH, 20 mM dithiothreitol (DTT) and 79 pi of the column fractions under test. After 30 min, Rubisco was added and after a further 30 min its activity was measured by the addition of COz and ribulose 1, 5 blsphosphate. The amount of carboxylation was measured from the - C remaining after evaporation of the acidified reaction mixture to dryness. 

Maximum rates of photorespiratory carbon dioxide formation in C3 plants are of the order of 40 micromoles per hour per mg chlorophyll, corresponding to 80 microequivalents of protons and phosphoglycollate per hour per mg chlorophyll formed in the stroma. The lysis of water by photosystem II also theoretically produces two protons, but these cannot represent a net source of acidity in the chloroplast, other than extremely transiently, since two protons are simultaneously consumed there in the subsequent formation of NADPH and reduced carbon compounds in the stroma. 

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