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• L-fucose isomerase was characterized from Caldanaerobius polysaccharolyticus. • Capo-LfIase showed maximum activity at 55 °C with melting temperature T m 82.3 °C and pH 6.5. • The recombinant Capo-LfIase showed 108.2 U mg-1of specific activities towards L-fucose. • It produced 28.12% L-fuculose as the sole product from L-fucose. • Capo-LfIase displayed more than 50% of its original activity after incubation at 55 °C for 20 h. L-fuculose is a rare sugar that is useful for the agriculture and medicine industries. L-fucose isomerase (E.C.5.3.1.25), which is an aldose-ketose isomerase, plays a significant role in producing rare sugars. A recommended L-fucose isomerase gene was cloned from Caldanaerobius polysaccharolyticus and purified with a single band of 65 kDa using nickel-affinity chromatography, with a specific activity of 108.23 U mg−1. The native molecular mass existed with 214 kDa was a trimer. The purified enzyme showed a maximum activity in 1 mM Mn2+ at 55 °C and pH 6.5 with a melting temperature (T m) of 80.3 °C in the presence of one molecule per monomer. L-fucose isomerase from C. polysaccharolyticus (Capo-LfIase) exhibited the highest activity of L-fucose with K m , k cat and K cat / k m values of 94.2 mM, 23854 min−1 and 253.3 min−1 mM−1, respectively. Capo-LfIase showed more than 50% thermostability after 20 h of incubation at 45, 55, 65, 75 and 85 °C. The 9 putative active site residues of the L-fucose substrate were described using a homology model, and the results showed that Tyr440, Met185, Trp499 and Asn527 are the candidates of metal-binding residues, while Ser393, Glu337, Glu302, His528 and Asp361 would be involved in substrate binding. The conversion rate of L-fuculose from L-fucose was almost 28.2%, with 80 g L−1 L-fucose, and no byproduct was found. To the best of our knowledge, Capo-LfIase produces high yield of L-fuculose from L-fucose by enzymatic methods. [ABSTRACT FROM AUTHOR]

• A novel d -arabinose isomerase was characterized from Thermanaeromonas toyohensis. • The enzyme showed activity at 75 °C and pH 9.0 for both d -arabinose and l -fucose. • The specific activities 98 and 85.52 U mg−1 for d -arabinose and l -fucose, respectively. • The enzyme produced 27% (21 g L−1) d -ribulose and 24.88% (19.92 g L−1) l -fuculose. • Its half life at 75 °C was 10 h. d -Ribulose and l -fuculose are potentially valuable rare sugars useful for anticancer and antiviral drugs in the agriculture and medicine industries. These rare sugars are usually produced by chemical methods, which are generally expensive, complicated and do not meet the increasing demands. Furthermore, the isomerization of d -arabinose and l -fucose by D d -arabinose and l -fucose by d -arabinose isomerase from bacterial sources for the production of d -ribulose and l -fuculose have not yet become industrial due to the shortage of biocatalysts, resulting in poor yield and high cost of production. In this study, a thermostable d -ribulose- and l -fuculose producing d -arabinose isomerase from the bacterium Thermanaeromonas toyohensis was characterized. The recombinant d -arabinose isomerase from T. toyohensis (Thto-DaIase) was purified with a single band at 66 kDa using His-trap affinity chromatography. The native enzyme existed as a homotetramer with a molecular weight of 310 kDa, and the specific activities for both d -arabinose and l -fucose were observed to be 98.08 and 85.52 U mg−1, respectively. The thermostable recombinant Thto-DaIase was activated when 1 mM Mn2+ was added to the reactions at an optimum pH of 9.0 at 75 °C and showed approximately 50% activity for both d -arabinose and l -fucose at 75 °C after 10 h. The Michaelis-Menten constant (K m), the turnover number (k cat) and catalytic efficiency (k cat / K m) for d -arabinose/ l -fucose were 111/81.24 mM, 18,466/10,688 min−1, and 166/132 mM−1 min−1, respectively. When the reaction reached to equilibrium, the conversion rates of d -ribulose from d -arabinose and l -fuculose from l -fucose were almost 27% (21 g L−1) and 24.88% (19.92 g L−1) from 80 g L−1 of d -arabinose and l -fucose, respectively. [ABSTRACT FROM AUTHOR]

• L-Ribulose producing l -ribose isomerase was characterized from Cryobacterium sp. N21. • CrL-RIse showed maximum activity at 35 °C and pH 9.0 in glycine-NaOH (50 mmol) buffer. • CrL-RIse showed highest specific activity (54.96 U mg−1) with l -ribose as substrate as compared to other l -RIs. • The recombinant CrL-RIse produced 31 % l -ribulose as the sole product from l -ribose. l -Ribose isomerase (l RI) is an enzyme that can catalyze the reversible isomerization between l -ribose and l -ribulose. It can also perform the conversion between many aldoses into their corresponding ketoses. l -RI was produced from Cryobacterium sp. N21 (CrL-RIse), and l -ribose was utilized as a substrate. The recombinant l -RI gene was cloned and overexpressed from Cryobacterium sp. N21. The purification of CrL-RIse was performed by metal-affinity chromatography. The enzyme displayed a corresponding band with an approximate size of 35 kDa on the SDS-PAGE analysis. The protein for this gene contains 266 amino acids with an expected molecular weight (M w) of 29.6 kDa. The measured M w of CrL-RIse calculated by HPLC was 125 kDa. CrL-RIse was extremely active in glycine buffer at 35 °C, pH 9.0, showing a specific activity of 54.96 U mg−1. CrL-RIse displayed no major increase in activity with metal ions, excluding Mn2+. The estimated Km , K ca t , K cat /Km and V max values of CrL-RIse were 37.8 mM, 10,416 min−1, 275.43 min−1 mM−1, and 250 U mg−1, respectively. The rate of l -ribulose production was 31 % (6.24, 12.11, and 20.89 g L−1) at equilibrium by utilizing 20, 40, and 70 g L−1 of the substrate, respectively. The results indicated that CrL-RIse has the capability to manufacture l -ribulose from l -ribose. [ABSTRACT FROM AUTHOR]

• l -Ribulose producing l -ribose isomerase was characterized from Mycetocola miduiensis. • Mm-LRIse showed maximum activity at 40 °C and pH 7.5 in sodium phosphate (50 mM) buffer. • Mm-LRIse showed the highest specific activity (47.40 U mg−1) with l -ribose as substrate as compared to other l -RIs. • It produced 32 % l -ribulose as the sole product from l -ribose. An enzyme, l -ribose isomerase (l -RI), mostly catalyzes the isomerization of l -ribose and l -ribulose. These so-called rare sugars are essential for the treatment of cancer and other viral diseases. In the present study, l -ribose isomerase produced from a bacterium, Mycetocola miduiensis (Mm-LRIse), by using l -ribose as a carbon source. The recombinant l -ribose isomerase gene was cloned and overexpressed from M. miduiensis and purified with an exclusive band of 32 kDa by nickel-affinity chromatography. This gene possessed 267 amino acids protein having an estimated molecular weight of 29,568.17 Da. The native molecular weight of Mm-LRIse estimated by HPLC was 134.84 kDa. The recombinant l -ribose isomerase was highly active in sodium phosphate (50 mM) buffer at 40 °C and pH 7.5, showing the specific activity up to 47.40 U mg−1. Mm-LRIse showed no significant enhancement in activity with metallic ions except Mn2+ and Co2+. The values of Km , K ca t , K cat /Km and V max of Mm-LRIse against l -ribose substrate were 42.48 mM, 9259.26 min−1, 217.43 min−1 mM−1, and 277.78 U mg−1 respectively. At equilibrium, the l -ribulose transformation rate was nearly 32 % (6.34 g L−1) using 20 g L−1 of l -ribose. The results revealed that the Mm-LRIse enzyme has a potential for L-ribulose production from l -ribose. [ABSTRACT FROM AUTHOR]