Glucose-1,6-diphosphate ribose-5-phosphate

Phosphoglucomutase acts not only on D-glucose and D-mannose phosphates (see p. 204) but also on D-ribose phosphates, the interconversion of D-ribosyl phosphate and D-ribose 5-phosphate being similarly accelerated by D-glucose 1,6-diphosphate,193 which appears to generate D-ribose 1,5-diphos-phate as cofactor.199(a) (b) (o) D-Ribose 5-phosphate is formed from D-ribose and ATP in the presence of yeast ribokinase.m... 

D-ribose l-diphosphate,5-phosphate <38> (<38> activation, kinetics, much more effective than fructose 1,6-diphosphate or glucose 1,6-diphosphate [5]) [5]... 

Adenosine 2, 5 -bis(phosphate), A-34 Adenosine 3, 5 -bis(phosphate), A-35 Adenosine cyclic 2, 3 -(hydrogen phosphate), A-32 Adenosine cyclic 3, 5 -(hydrogenphosphate), C-162 Adenosine 3 -(dihydrogen phosphate), A-31 Adenosine 2 -(dihydrogen phosphate), A-45 Adenosine diphosphate glucose, A-36 Adenosine diphosphate ribose, A-37 Adenosine diphosphate, A-33 Adenosine 2, 5 -diphosphate, A-34 Adenosine 3, 5 -diphosphate, A-35 Adenosine 2, 5 -diphosphoric acid, A-34 Adenosine 3, 5 -diphosphoric acid, A-35 Adenosine 5 -monophosphate, A-44 Adenosine 5 -(pentahydrogen tetraphosphate), A-38 Adenosine phosphate, A-44 Adenosine 5"-phosphate, A-44 Adenosine 5"-pyrophosphate, A-33 Adenosine 5"-(tetrahydrogen triphosphate), A-39 Adenosine 5"-tetraphosphate, A-38... 

To summarize these observations First, the enzymes of this segment of the photosynthetic carbon reduction cycle are not controlled co-ordinately a single inductive step does not appear to affect the activity (and presumably the production) of these three enzymes in the same way. Second, the kinds of control mechanisms which appear to occur here are (1) a direct and prompt effect of illumination, reflected in the rapid increase in ribulose-diphosphate carboxylase activity, and (2) a more indirect kind of control, possibly involving induction of the other enzymes (e.g., ribose-phosphate isomerase) by small molecules produced in photosynthesis. Unfortunately, it has not been possible to demonstrate an increase in the level of either the isomerase or kinase by administration of glucose and some other carbohydrates to etiolated leaves in darkness. 

Nicotinamide adenine dinucleotide (NAD) Fructose 1,6-diphosphate Glucose-6-phosphate Isopentenyl pyrophosphate Ribose-6-phosphate-l-pyrophosphate... 

Phosphoglucomutase (EC 2.7 5.l) slowly converts R-l-P to ribose-5-phosphate. A mixture of 35 mM R-l-f O J-P, 17mM R-l-[ L 0l(]-P and less than lmg glucose-1,6-diphosphate at pH 7 33 was equilibrated with phosphoglucomutase (Sigma, P3397, rabbit muscle), at 25°C for 3 Hr. The 31p NMR spectrum was recorded at pH 7 37- The enzyme converted ca. 20 to a mixture of ribose-5-phosphate l Ol (resonance identified by addition of authentic material) and I80I803 species. This demonstrated that the enzyme catalyzed formation of the 0-P bond. 

PG = 3-phosphoglyceric acid G3P = glyceraldehyde 3-phosphatc DHAP = dihydroxyacetone phosphate FDP = fructose 1,6-diphosphate F6P = fructose 6-phosphate G6P = glucose 6-phosphate E4P = erythrose 4-phosphate X5P = xylulose 5-phosphate SDP = sedoheptulose 1,7-diphosphaie S7P = sedoheptulose 7-phosphate R5P = ribose 5-phosphate Ru5P = ribulose 5-phosphate RuDP = ribulose 1,5-diphosphate... 

Sugar phosphates D-Ribose-5-phosphate D-Ribose-1,5-diphosphate D-Fructose-1 -phosphate D-Fructose-6-phosphate D-Fructose-1,6-diphosphate D-Glucose-1-phosphate D-Glucose-6-phosphate D-Mannose-6-phosphate D-Galactose-6-phosphate... 

Aldoses react with ATP in a phosphotransferase-catalyzed reaction (C 1.1) either to sugar-l-phosphates, e.g., D-galactose-l-phosphate and L-arabinose-1-phosphate, or to sugar-co-phosphates, e.g., D-glucose-6-phosphate (Fig. 27), D-mannose-6-phosphate, D-galactose-6-phosphate, and D-ribose-5-phosphate. Aldose-l-phosphates may also be formed from co-phosphates by mutases (Fig. 27) with 1,co-diphosphates as intermediates. 

Glyceraldehyde 3-phosphate, it will be recalled (Scheme 11.13), is a progenitor of glucose-6-phosphate, which, via the pentose phosphate pathway, is also (i.e., in addition to the Calvin cycle) on the path to ribulose-5-phosphate. Now, via the common enol, ribulose-5-phosphate is readily converted to ribose-5-phosphate (EC 5.3.1.6), which is then bisphosphorylated (EC 2.7.6.1) to the a-diphosphate so that a leaving group is in place that will allow replacement by the terminal amido function of glutamine (Gin, Q) on its way to glutamate (Glu, E) with the formation of 2-aminoribose-5-phosphate. 

Figure 5.27 Relative fluorescence increase (F/Fo) of HPTS (4.0 x lO" M) with viol-ogen quenchers (3,3 - (white bars), 4,3 - (gray bars), and 4,4 -viologen (black bars) 5.0 x lo M) after adding analytes. Bottom ortho-WN receptors. Top BV quenchers. Analytes at a final concentration of 1.0 X10" M (phosphate buffer, pH 7.4,39 mM) (l) glucose-l-phosphate, (2) glucose-6-phosphate, (3) fructose-6-phosphate, (4) fructose-1,6-diphosphate, (5) ribose-5-phosphate, (6) glucose, (7) fructose, (8) ribose, (9) AMP, (10) ADP, (11) ATP, and (12) GTP. Errors are given in a 95.5% confidence interval.

Fig. 36. The Calvin cycle (black lines) and pentose phosphate cycle (red lines). PGA = 3-Phosphoglyceric acid, PGAL = 3-phosphoglyceraldehyde, Rib. = ribose-5-phosphate, Xyl = xylulose-5-phosphate, Ru-diP = ribulose-1,5-diphosphate, C4 = erythrose-4-phosphate, FDP = fructose-1,6-diphosphate. A few of the enzymes participating are encoded, 1 = carboxydismutase, 2 = triose phosphate dehydrogenase, 3 = triose phosphate isomerase, 4 = aldolase, 5 = phosphatase, 6 = phosphoglucoisomerase. Details of the conversion of glucose-6-P into ribulose-5-P are given in Fig. 43. It should be pointed out that the pentose phosphate cycle presents only here and there a true reversal of the Calvin cycle. In many instances the mechanisms and enzymes are different.

Tissues which are more active in the synthesis of lipids than nucleotides require NADPH rather than ribose moieties. In such tissues, e.g. adipose tissue, the ribose 5-phosphate enters a series of sugar interconversion reactions which connect the pentose phosphate pathway with glycolysis and gluconeogenesis. These interconversion reactions constitute the non-oxidative phase of the pathway (Figure 11.14) and since oxidation is not involved, NADPH is not produced. Two enzymes catalyse the important reactions transketolase which contains thiamin diphosphate (Figure 12.3a) as its prosthetic group and transaldolase. Both enzymes function in the transfer of carbon units transketolase transfers two-carbon units and transaldolase transfers three-carbon units. The transfer always occurs from a ketose donor to an aldose acceptor. The interconversion sequence requires the oxidative phase to operate three times, i.e. three molecules of glucose 6-phosphate yield three molecules of ribulose 5-phosphate. 

A type of reaction which is applicable in many cases is the phosphorylation with ATP using different kinases. In this manner many esters can be obtained from the free sugars such as glucose 6-phosphate, mannose 6-phosphate, fructose i-phosphate, fructose 6-phosphate, fructose i,6-diphosphate, galactose i-phosphate, galactosamine i-phosphate, gluconic acid 6-phos-phate, ribose 5-phosphate and ribulose 5-phosphate. A special case of enzymic phosphorylation in which a pyrophosphate residue is transferred from ATP is the following reaction ... 

When the second substituent in the phosphate is another phosphate instead of an alkyl group, formation of the cyclic compound occurs under mild alkaline treatment. Thus, uridine diphosphate glucose yields uridine monophosphate and glucose cyclic i 2-phosphate and 5-phosphoribosyl P5U ophosphate gives ribose 5-phosphate cyclic i 2-phosphate and inorganic phosphate. Similar changes occur with cytidine diphosphate ribitol and cytidine diphosphate glycerol . 

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