• Microbiology and Biotechnology Letters
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• v.33 no.2
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• pp.106-111
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• 2005

To investigate the substrate variety of a putative non-metal dependent isomerase, the tagatose-6-phosphate isomerase (E.C. 5.3.1.26) structural genes (lacB; 510bp and lacA; 430bp) of Staphylococcus aureus were subcloned and co-expressed. Based on the substrate configuration, various aldoses were surveyed for substrate of ketose isomerization. Among the 10 aldoses tested, D-ribose and D-allose were isomerized by the enzyme. The subunit A and B showed more than $95\%$ activity for D-ribose and $75\%$ for D-allose in the presence of 1mM EDTA compared with non-EDTA conditions, which implying tagatose-6-phosphate isomerase is a non-metal dependent isomerase. Each of subunit A or subunit B alone showed no activity for any of the substrates tested. The affinity constant ($K_m$) of tagatose-6-phosphate isomerase against D-ribose and D-allose were 26 mM and 142 mM, respectively.

• Journal of Microbiology and Biotechnology
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• v.28 no.7
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• pp.1122-1132
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• 2018

In this study, we attempted to find new and efficient microbial enzymes for producing rare sugars. A ribose-5-phosphate isomerase B (OsRpiB) was cloned, overexpressed, and preliminarily purified successfully from a newly screened Ochrobactrum sp. CSL1, which could catalyze the isomerization reaction of rare sugars. A study of its substrate specificity showed that the cloned isomerase (OsRpiB) could effectively catalyze the conversion of $\text\tiny{L}$-rhamnose to $\text\tiny{L}$-rhamnulose, which was unconventional for RpiB. The optimal reaction conditions ($50^{\circ}C$, pH 8.0, and 1 mM $Ca^{2+}$) were obtained to maximize the potential of OsRpiB in preparing $\text\tiny{L}$-rhamnulose. The catalytic properties of OsRpiB, including $K_m$, $k_{cat}$, and catalytic efficiency ($k_{cat}/K_m$), were determined as 43.47 mM, $129.4sec^{-1}$, and 2.98 mM/sec. The highest conversion rate of $\text\tiny{L}$-rhamnose under the optimized conditions by OsRpiB could reach 26% after 4.5 h. To the best of our knowledge, this is the first successful attempt of the novel biotransformation of $\text\tiny{L}$-rhamnose to $\text\tiny{L}$-rhamnulose by OsRpiB biocatalysis.

• Journal of The Korean Society of Grassland and Forage Science
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• v.25 no.4
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• pp.287-296
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• 2005

To investigation protein expression pattern in rice leaves exposed to cold stress, the soluble proteins extracted from leaf tissue were fractionated with $15\%$ PEG and separated by two-dimensional polyacrylamide gel electrophoresis (2-DE). Differentially expressed proteins were identified by peptide mass fingerprinting using matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Eight proteins up-regulated and 10 down-regulated were found in $15\%$ PEG supernatant fraction. In addition, 13 proteins up-regulated and 14 down-regulated were found in $15\%$ PEG pellet fraction. It was identified the differentially expressed proteins in $15\%$ PEG supernatant fraction as pimerase/dehydratase fructokinase, ribose-5-phosphate isomerase (Rpi), chaperonin 21 precursor, probable photosystem II oxygen-envolving complex (PS II OEC) protein 2 precursor and thioredoxin h-type (Trx-h) and those in $15\%$ PEG pellet fraction as OSINBb0059K02.15, hypothetical protein, putative mitogen-activated protein kinase kinase (MAPKK), beta 7 subunit of 205 proteasome, ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit. These proteins are involved in metabolism, energy, protein synthesis, disease/defense and signal transduction-related proteins.