D-Erythro-pentulose

In contrast, much information is available about five-carbon sugars. The most widely studied D-pentoses, D-ribose and 2-deoxy-D-erythro-pentose, are discussed in Section VII (see p. 86). The aldopentoses can form either furanose or pyranose rings, and both structures are known, although not in the same crystal. Crystallographic data have not been obtained for either of the 2-pentuloses D-erythro- and D-threo-2-pentulose ( D-ribulose and D-xylulose ), as they are syrupy. 

Subsequent studies196 on crystalline transketolase have revealed the presence of a contaminating enzyme termed pentulose 5-phosphate waldenase (or epimerase) the presence of which had led to the erroneous conclusion that d-erythro-pentulose 5-phosphate was the substrate for transketolase. d-erythro-Pentulose 5-phosphate is virtually unattacked by transketolase prepared from spinach or liver. In subsequent discussions of experiments involving the use of transketolase, in this article, the enzymic reactions must be viewed as the result of action of transketolase and pentulose 5-phosphate waldenase (epimerase). 

D-erythro-Pentulose 5-phosphate (XLIV) has been formed by the action of transketolase on hydroxypyruvate (XLII) and D-glycerose 3-phosphate, the hydroxypyruvate being decarboxylated196 to active glycolaldehyde which then reacts with the triose phosphate by an acyloin reaction.28 The active glycolaldehyde is also formed from L-glycero-tetrulose, d-altro-heptulose 7-phosphate, D-fructose 6-phosphate, and D-i/ireo-pentulose 5-phosphate and it reacts with various aldehydes (acceptors) to give ketoses.198, 200 Thus, substitution of L-gfh/cero-tetrulose for hydroxypyruvate in the above experiment also resulted in formation of D-en/i/iro-pentulose... 

D-xylo-Hexulose D-erythro-Pentulose (D-Fructose) (D-Ribulose)... 

Decarboxylation must lead to incorporation of a proton from the solvent. The oxidative decarboxylation of 6-O-phosphono-D-gluconate gives D-erythro-pentulose-1 (S)-t 5-phosphate (with inversion of configuration).45 The R-isomer can be obtained46 from D-ribose 5-phosphate by using D-ribose 5-phosphate ketol isomerase (E.C. 5.3.1.6). 

For D-glucose-grown yeast, partly purified enzyme catalyzes erythritol — g/ycero-tetrulose, D-arabinitol - D-threo-pentulose, xylitol — threo-pentulose, ribitol — erythro-pentulose, D-glucitol — fructose, galactitol — tagatose, D-mannitol —> fiructose.612... 

Extracts catalyze D-arabinitol D-erythro-pentulose, and reduction of NADP with xylitol.613... 

D-erythro-pentulose 5-phosphate - pentose-cycle reactions... 

The D-2-pentuloses, o-erythro-l-ptn lulose (D-ribulose, 12) and o-threo-l-pentulose (D-xylulose, 13) are able to cyclize as 2-pentulofuranoses. The 2-ketopentoses are important metabolic intermediates in glycolysis.11... 

Occurrence. D-f/treo-Pentulose 5-phosphate (d-xylulose 5-phosphate) is an intermediate in the metabolism of xylose in bacteria, and is also formed from d-erythro-pentulose 5-phosphate in the presence of an epimerase.57 D- /m o-PcnLulose has been found in a lipopolysaccharide from Pseudomonas diminuta, from which it was obtained after hydrolysis by mild acetic acid as used to release lipid A.58 It was also found in the LPS of a Yersinia enterocolitica serologic variant.59... 

D-erythro-Pentose, 2-deoxy- deoxyribose D-erythro-2-Pentulose xyluiose ... 

D-erythro-2-Pentulose = D-Ribulose xylulose H0CH2-C0-(CH0H)2-CH20H II.A-5... 

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