Search

Starch, whey or hemicellulosic waste can be used as a raw material for the industrial production of rare sugars.D-Glucose from starch, whey and hemicellulose, D-galactose from whey, and D-xylose from hemicellulose are the main starting monosaccharides for production of rare sugars. We can produce all monosaccharides; tetroses, pentoses and hexoses, from these raw materials. This is achieved by using D-tagatose 3-epimerase, aldose isomerase, aldose reductase, and oxidoreductase enzymes or whole cells as biocatalysts. Bioproduction strategies for all rare sugars are illustrated using ring form structures given the name Izumoring. [Copyright &y& Elsevier]

Alcohol dehydrogenase was covalently conjugated with three different oxidized carbohydrates i.e., glucose, starch and pectin. All the carbohydrates inhibited the enzyme. The inhibition was studied with respect to the inhibition rate constant, involvement of thiol groups in the binding, and structural changes in the enzyme. The enzyme activity decreased to half of its original activity at the concentration of 2 mg/mL of pectin, 4 mg/mL of glucose and 10 mg/mL of starch within 10 min at pH 7. This study showed oxidized pectin to be a potent inhibitor of alcohol dehydrogenase followed by glucose and starch. Along with the aldehyde-amino group interaction, thiol groups were also involved in the binding between alcohol dehydrogenase and carbohydrates. The structural changes occurring on binding of alcohol dehydrogenase with oxidized carbohydrates was also confirmed by fluorescence spectrophotometry. Oxidized carbohydrates could thus be used as potential inhibitors of alcohol dehydrogenase. [ABSTRACT FROM AUTHOR]

d-Arabinose isomerase from Klebsiella pneumoniae 40bXX was purified 12-fold with a 62.5% yield indicated by its electrophoretic homogeneity. The purified enzyme showed the highest activities toward d-arabinose and l-fucose as substrates at optimum conditions (50 mM glycine–NaOH, pH 9.0, 40°C). The enzyme had a broad range of substrate specificities toward various d/l-aldoses, i.e., d-arabinose, l-fucose, d/l-xylose, d-mannose, d/l-lyxose, l-glucose, d-altrose and d/l-galactose. The equilibrium ratios between d-arabinose and d-ribulose, l-fucose and l-fuculose, d-altrose and d-psicose, and l-galactose and l-tagatose were 90:10, 90:10, 13:87 and 25:75, respectively. Using a combination of the immobilized d-tagatose 3-epimerase and d-arabinose isomerase, we achieved the production of d-altrose from d-fructose in a batch reactor. We successfully produced approximately 12 g of d-altrose from 200 g of d-fructose in a reaction series with an overall yield of 6%. The product obtained was confirmed to be d-altrose by HPLC and 13C-NMR. To the best of our knowledge, this is the first report on the production of d-altrose from a cheap sugar, d-fructose, using an enzymatic method. [Copyright &y& Elsevier]

Mass production of a rare aldohexose d-allose from d-psicose was achieved in a batch reaction by crude recombinant l-rhamnose isomerase (l-RhI) cross-linked with glutaraldehyde. The d-psicose substrate was, in turn, mass produced from a naturally abundant ketohexose d-fructose by immobilized recombinant d-tagatose 3-epimerase (d-TE). At an equilibrium state, 25% of d-psicose was isomerized to d-allose, that is, 25 g of d-allose was obtained from 100 g of d-psicose. The d-allose product was easily separated and crystallized from the reaction mixture that contains 25%d-allose, 8%d-altrose and 67%d-psicose using ethanol. Empirically, approximately 338 g, that is, 90% of a theoretical overall yield for the purification of pure d-allose crystals was produced from 1.5 kg of d-psicose within 30 d using a constructed bioreactor. The cross-linked enzyme had an operative half-life of two months after repeated usages. [Copyright &y& Elsevier]

Wild-type strain of Pseudomonas cichorii ST-24 was unable to grow on D-psicose and inductively produced D-tagatose 3-epimerase (D-TE) with D-tagatose as an inducer. We have isolated a constitutive mutant, designated strain Ka75, which had acquired a new ability to grow on a mineral salts medium containing D-psicose as a sole carbon source. The D-psicose-metabolizing mutant synthesized a high level of D-TE. When grown on the culture medium supplemented with Mn2+, the mutant strain produced around 250-fold higher activity than did the parent strain. Enzymatic properties of the constitutive enzyme were similar to those of the wild-type. Using the immobilized D-TE and recombinant L-rhamnose isomerase (L-RhI) from Escherichia coli strain JM109, a two-step enzymatic reaction was performed for massproduction of a rare aldo-hexose monosaccharide, L-galactose, from a common one, L-sorbose. In the first step, L-sorbose was epimerized to L-tagatose in a yield of 28%. The L-tagatose obtained was utilized as a starting material for L-galactose preparation by the immobilized L-RhI. At equilibrium, approximately 30% L-tagatose was isomerized to L-galactose. Finally, 7.5 g of L-galactose was obtained from 100 g of L-sorbose, viz an overall yield of 7.5%. The product obtained was purified and identified to be L-galactose by specific optical rotation and high performance liquid chromatography (HPLC) analysis, and was ultimately confirmed by 13C nuclear magnetic resonance (13C NMR) and IR spectra. [Copyright &y& Elsevier]