Pentulose enzymic synthesis

On the other hand, as mentioned in the preceding subsection, a preparative-scale enzymic synthesis of 1-deoxy-D-r/ireo-pentulose can be achieved, according to Reaction 1, in the presence of an extract of B. pumilus. Obviously, this raises the question of the relevance of Eq. 1 to the production of the pentulose in microorganisms. Acetoin in Reaction 1 could be replaced by 3-hydroxy-3-methyl-2-butanone (then the by-product is acetone). More interestingly, it can be also replaced by pyruvate, then the pentulose is synthesized according to Reaction 3 ... 

The enzymic synthesis of D-plant polysaccharides. Xylose isomerase has been found in Lactobacillus pento-... 

Preparation. D-m7//ro-2-Pentulose (12) has been synthesized from D-arabinose by isomerization with pyridine, followed by isolation as the crystalline (o-nitrophenyl)hydrazone.54 Enzymic synthesis provides D-eiyf/tro-2-pentulose by oxidation of ribitol with NAD-dependent ribitol dehydrogenase55 or from D-arabinitol with D-arabinitol dehydrogenase.56... 

Treatment of potato peels with phosphorylase gave D-glucose which was phosphorylated to yield D-glucose 1-phosphate of commercial grade. A preparative enzymic synthesis of D-threo-2-pentulose... 

An extract from the soluble stromal proteins of purified and intact spinach-leaf chloroplasts was prepared by lysis of the cells in buffer, centrifugation of the suspension of broken cells, and concentration of the supernatant with removal of insoluble material. This extract contained all of the enzymes involved in the condensation of the cyclic moieties of thiamine, thiazole, and pyramine. Thus, the synthesis of thiamine in this extract following the addition of pyramine and putative precursors was a proof that the system had the possibility of building the thiazole. It was found that L-tyrosine was the donor of the C-2 carbon atom of thiazole, as in E. coli. Also, as in E. coli cells, addition of 1 -deoxy-D-f/irco-pen-tulose permitted synthesis of the thiamine structure. The relevant enzymes were localized by gel filtration in a fraction covering the 50- to 350-kDa molecular-mass range. This fraction was able to catalyze the formation of the thiazole moiety of thiamine from 0.1 -mM 1-deoxy-D-t/ireo-pentulose at the rate of 220 pmol per mg of protein per hour, in the presence of ATP and Mg2+. 

The thiazole ring is synthesized from a pentulose or deoxypentulose 5-phosphate and either glycine or tryptophan, depending on the organism. Incorporation of sulfur leads to formation of hydroxymethyl thiazole, which is then phosphorylated. The sulfur comes from cysteine and is incorporated by formation of a thiocarboxylate at the carboxyl terminal of the enzyme, unlike biotin synthesis (Section 11.1.1), where an iron-sulfur cluster at the active site of the enzyme is the donor. 

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