Ribulose=5-phosphate

In the biosynthesis of the thia2ole, cysteine is the common sulfur donor. In yeasts, the C-2 and N may be suppHed by glycine, and the remaining carbons byD-ribulose-5-phosphate [108321-99-9] (50). In anaerobic bacteria, the C-2 andN maybe recmited from tyrosine and the carbons from D-l-deoxyxylulose [16709-34-5] (51), whereas in aerobic bacteria the C-2 and N maybe derived from glycine, as in yeasts 7 (74—76,83—86) (see Fig. 9). 

As discussed in Section 22.7, illumination of chloroplasts leads to light-driven pumping of protons into the thylakoid lumen, which causes pH changes in both the stroma and the thylakoid lumen (Figure 22.27). The stromal pH rises, typically to pH 8. Because rubisco and rubisco activase are more active at pH 8, COg fixation is activated as stromal pH rises. Fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, and glyceraldehyde-3-phosphate dehydrogenase all have alkaline pH optima. Thus, their activities increase as a result of the light-induced pH increase in the stroma. 

In the pentose plu phatc pathway for degrading sugars, ribulose 5-phosphate is converted to ribose 5-phosphale. Propose a mechanism for the isomerization. 

Similar to DHAP aldolases, the 3-hexulose 6-phosphate aldolase found in Methylomonas Ml 5 is highly specific for the aldol donor component D-ribulose 5-phosphate, but accepts a wide variety of aldehydes as replacement for formaldehyde as the acceptor. With propanal,... 

Ribulose 5-phosphate is the substrate for two enzymes. Ribulose 5-phosphate 3-epimerase alters the configuration about carbon 3, forming another ketopentose, xylulose 5-phosphate. Ribose 5-phosphate ketoisom-erase converts ribulose 5-phosphate to the corresponding aldopentose, ribose 5-phosphate, which is the precursor of the ribose required for nucleotide and nucleic acid synthesis. Transketolase transfers the two-carbon... 

RIbulose 5-phosphate------RIbulose 5-phosphate-----RIbulose 5-phosphate-... 

Dehydrogenation of 6-phosphogluconate to ribulose 5-phosphate. This reaction is catalyzed by 6-phosphogluconate dehydrogenase according to the scheme ... 

Ribulose 5-phosphate is capable of a reversible isomerization to other pentose phosphates-xylulose 5-phosphate and ribose 5-phosphate. These reactions are catalyzed by two respective enzymes, viz., pentose-phosphate epimerase and pentose-phosphate isomerase, according to the scheme below ... 

Two other pentose phosphates (ribose 5-phosphate and xylulose 5-phosphate), which are derived from ribulose 5-phosphate, are important for the subsequent reaction of the cycle. Two molecules of... 

M12. McNair Scott, D. B., and Cohen, S. S., The oxidative pathway of carbohydrate metabolism in Escherichia coli. 5. Isolation and identification of ribulose-5-phosphate produced from 6-phosphogluconate by the dehydrogenases of Escherichia coli. Biochem. J. 65, 686-689 (1957). 

The PPP has two chemical phases an initial irreversible oxidative phase when G6P is decarboxylated and oxidized to form ribulose-5-phosphate (Ru-5-P) followed by a more complicated but reversible non-oxidative phase involving interconversions of phosphorylated monosaccharides with four, five, six or seven carbon atoms. The... 

The second part consists of a series of reactions in which ribulose 5-phosphate is reconverted back to glucose 6-phosphate (i.e. 5C 6C ) (Figure 6.20) (Appendix 6.8). Some key processes that depend on NADPH, and therefore the pentose phosphate pathway, are identified in Table 6.3 and presented in Figure 6.21. 

The oxidative segment of the PPP converts glucose 6-phosphate to ribulose 5-phosphate. One CO2 and two NADPH+H" are formed in the process. Depending on the metabolic state, the much more complex regenerative part of the pathway (see B) can convert some of the pentose phosphates back to hexose phosphates, or it can pass them on to glycolysis for breakdown. In most cells, less than 10% of glucose 6-phosphate is degraded via the pentose phosphate pathway. 

The last enzyme in the oxidative part is phosphogluconate dehydrogenase [3], which releases the carboxylate group of 6-phosphogluconate as CO2 and at the same time oxidizes the hydroxyl group at C3 to an 0x0 group. In addition to a second NADPH+H", this also produces the ketopentose ribulose 5-phosphate. This is converted by an isomer-ase to ribose 5-phosphate, the initial compound for nucleotide synthesis (top). 

T) Ribulose 1,5-bisphosphate (2 Carbon dioxide (3) 3-Phosphoglycerate (4 1,3-Bisphosphoglycerate (5 Clyceraldehyde 3-phosphate Dihydroxyacetone phosphate (7) Fructose 1,6-bisphosphate Fructose 6-phosphate (9) Erythrose 4-phosphate Sedoheptulose 1,7-bisphosphate ( Sedoheptulose 7-phosphate Xylulose 5-phosphate Ribose 5-phosphate Ribulose 5-phosphate ( ) Glucose 6-phosphate... 

This enzyme [EC 5.3.1.13] catalyzes the interconversion of D-arabinose 5-phosphate to D-ribulose 5-phosphate. 

This enzyme [EC 5.3.1.24], also known as /V-(5 -phos-phoribosyl)anthranilate isomerase, catalyzes the interconversion of /V-(5-phospho-/3-D-ribosyl)anthranilate and l-(2-carboxyphenylammo)-l-deoxy-D-ribulose 5-phosphate. In some organisms, this enzyme is part of a multifunctional protein, together with one or more components of the system for the biosynthesis of tryptophan (anthranilate phosphoribosyltransferase, indole-3-glycerol-phosphate synthase, anthranilate synthase, and tryptophan synthase). 

This enzyme [EC 1.1.1.137] catalyzes the reaction of d-ribitol 5-phosphate with NAD(P)+ to produce D-ribulose 5-phosphate and NAD(P)H. 

This enzyme [EC 5.1.3.1] (also known as phosphoribu-lose epimerase, erythrose-4-phosphate epimerase, and pentose-5-phosphate 3-epimerase) catalyzes the interconversion of D-ribulose 5-phosphate and D-xylulose 5-phosphate. The enzyme can also act on D-erythrose 4-phosphate. 

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