Tetrose phosphate

I, 7-diphosphate.170 1 (f> This tetrose phosphate is involved with phosphoenol pyruvate in the formation of shikimic acid via 3-deoxy-2-keto-D-ara6ino-heptonic acid 7-phosphate and, hence, of aromatic compounds.170(d) A synthesis of the tetrose phosphate has been described.170 1 Aldolase shows a high affinity for the heptulose diphosphate and, compared with that for D-fructose 1,6-diphosphate, the rate of reaction is about 60 %. The enzyme transaldolase, purified 400-fold from yeast, catalyzes the following reversible reaction by transfer of the dihydroxyacetonyl group.l70(o>... 

The above transketolase and transaldolase reactions were found inadequate to explain the metabolism of D-ribose 5-phosphate, because of the non-accumulation of tetrose phosphate, the 75 % yield of hexose phosphate, and the results of experiments with C14 (the distribution of which differed markedly from the values predicted for such a sequence). 24(b) Thus, with D-ribose-l-C14, using rat-liver enzymes, any hexose formed should have equal radioactivity at Cl and C3, whereas, actually, 74% appeared at Cl. Furthermore, D-ribose-2,3-Cl42 should have given material having equal labels at C2 and C4 in the resultant hexose, whereas, in fact, it had 50% of the activity at C4, C3 was nearly as active as C2, and Cl had little activity. Similar results were obtained with pea-leaf and -root preparations.24 The following reactions, for which there is enzymic evidence,170(b) were proposed, in addition to those involving D-aftro-heptulose, to account for these results.24(b) (o) 200... 

The tetrose phosphate (LVI) acts as an acceptor for active glycolaldehyde derived from n-i/ireo-pentulose 5-phosphate (LII), and thus, in the presence of transketolase, yields D-fructose 6-phosphate (LV) and D-glyc-erose 3-phosphate. The reverse of this reaction has been observed.200 The... 

The same net result will be obtained if tetrose phosphate is generated by Reactions (1), (2b), and (3). In either case, two thirds of the tetrose phosphate molecules will be derived from Reaction (1), or from Reactions (1) plus (2b), and they will have the labeling sequence G-3,4,5,6 (starting with Cl of the tetrose). One third of the tetrose phosphate molecules, being derived from reaction (3), will have the labeling sequence... 

These calculated values are shown in Table I and are there compared with the observed ratios of activities of n-glucose carbon atoms incorporated into carbon atoms 3,4,5, and 6 of shikimate. It is evident that these carbon atoms of shikimate originate in the same carbon atoms of D-glucose as are predicted for carbon atoms 1,2,3, and 4 of tetrose phosphate, respectively. Carbon atom 3 of shikimate has approximately the same G-3,4/G-2 ratio as is calculated for G-3/G-2 in Cl of tetrose phosphate. However, the ratio... 

Comparison of Activities from Labeled D-Ghicose Calculated for Tetrose Phosphate, and Found in Carbon Atoms S,4,S, and 8 of Shikimate... 

If, now, the n-fructose 6-phosphate, labeled as predicted from the operation of Reaction (4), is introduced as a substrate into Reactions (1), (2), and (3), carbon atoms 2,3, and 4 of the tetrose produced will have more isotope from G-3,2,1 than previously calculated (see Table I) the G-3/G-2 ratio in Cl of the tetrose will be unaffected. It may be seen from Table I that the concentration of G-3,2,1 in the bottom three carbon atoms of the tetrose phosphate, expectedfrom Reactions (1), (2), and (3) alone, is 1/(1 + 5), or 17 per cent. The concentration of G-3,2,1 in carbon atoms 4,5, and 6 of shikimate is 1/(1 -h 2.5), or approximately 29 per cent. If it be assumed that this increase in concentration of G-3,2,1 (to nearly double the expected value) is due to the exchange postulated in Reaction (4), it follows that almost half of the n-fructose 6-phosphate had been affected by this reaction. The relatively high incorporation of G-3,2,1 into carbon atoms... 

Rifamycin S derived from [l- C]glycerate showed enhanced n.m.r. signals for C-3 and C-8 which is consistent with incorporation by way of intermediates on the shikimate pathway (Scheme 22). ° Greater enhancement of C-8 by [l- C]glycerate and of C-1 by [l- C]glucose was observed, compared respectively with C-3 and C-10. This indicates that C-1 derives from the methylene carbon of phosphoenol-pyruvate rather than C-4 of tetrose phosphate and that C-8 derives from the carboxy-group of phosphoenolpyruvate. It follows then that C-9 and C-10 of rifamycin S (193) would be the location of the double bond of a dehydroshikimate intermediate. Michael addition to this double bond as in (194) allows completion of the naphthoquinone moiety of rifamycin S in an analogous fashion to the formation of the menaquinones. ... 

Sedoheptulose Diphosphate. The transaldolase reaction requires phos-phoglyceraldehyde, which has become available as a sjmthetic compound only recently. A convenient method for supplying those phosphate is to add fructose diphosphate and aldolase. When this device was used in a study of the transaldolase reaction, the reaction products of the system containing both aldolase and transaldolase, and hexose diphosphate and sedoheptulose phosphate were expected to include tetrose phosphate, as shown in equation (VI) above. Tetrose phosphate failed to accumulate, however. Instead, sedoheptulose-1,7-diphosphate was found to accumulate as a result of condensation of the tetrose ester with dihydroxy-acetone phosphate in the presence of aldolase. This diphosphate reacts rapidly with aldolase, and it is not known whether it can react in any other systems, or only shuttles back and forth in response to changes in tetrose phosphate level. 

D-Erythrose 4-phosphate has been synthesized and shown to condense with dihydroxyacetone phosphate in the presence of aldolase to give a heptulose diphosphate with properties similar to the one described above 229 ), The synthetic tetrose phosphate is optically inactive, and is decomposed by acid at a rate similar to glyceraldehyde 3-phosphate. 

The tetrose phosphate formed in the preceding reaction (29) was identified as D-erythrose 4-phosphate (96) on the basis of its participation in several reactions. The tetrose phosphate was found to react in an aldolase-catalyzed reaction with dihydroxyacetone phosphate to yield D-sedohep-... 

Aldolase catalyses the formation of heptulose diphosphate from a molecule of tetrose phosphate and a molecule of triose phosphate (C + C3 = C7). Phosphatase converts the heptulose-PP to heptulose-P which, with a further molecule of triose-P, in the presence of transketolase, forms a molecule of ribose-P and a molecule of ribulose-P (Q + Cj = 2Cj). The isomerase for pentose phosphates converts this mixture to ribulose-P which, in the presence of ATP and phosphopentokinase, gives ribulose-PP. 

Bacteria often use the Meyerhof sequence, but at least two alternative pathways have been found. In one of these (the pentose phosphate pathway) glucose-6-phosphate is oxidized to ribulose-5-phosphate, two molecules of which are quickly changed to one molecule each of glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate. These phosphates then yield fructose-6-phosphate and a tetrose phosphate. In the other (the 2-keto-3-deoxy-6-phosphogluconate pathway), glucose is oxidized to gluconate by a primitive route without prior phosphorylation. The non-Meyerhof routes are favoured by those bacteria, such as the pseudomonads and aerobacters, which cannot utilize glucose-6-phosphate. 

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