PubMed · 9434470
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T Akira, H Naka. 1997. [SG-210].. https://pubmed.ncbi.nlm.nih.gov/9434470/
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A xylose reductase (XR) gene was identified from the Neurospora crassa whole-genome sequence, expressed heterologously in Escherichia coli, and purified as a His6-tagged fusion in high yield. This enzyme is one of the most active XRs thus far characterized and may be used for the in vitro production of xylitol.
Studies have shown that polymorphisms located at positions -106 and approximately -2100 base pairs (5'ALR2) in the regulatory region of the aldose reductase gene are associated with susceptibility to microvascular complications in patients with diabetes. The aim was to investigate the functional roles of these susceptibility alleles using an in vitro gene reporter assay. Susceptibility, neutral and protective 5'ALR2/-106 alleles were transfected into HepG2 cells and exposed to excess D-glucose (D-glucose at final concentrations 14 or 28 mmol/l). Transcriptional activities were determined using a dual luciferase reporter gene assay. The "susceptibility alleles" Z-2 with C-106 had the highest transcriptional activity when compared with the "protective" combination of Z+2 with C-106 alleles (58.7+/-9.9 vs. 10.1+/-0.7; P<0.0001). Those constructs with either the Z or Z-2 in combination with the C-106 allele had significantly higher transcriptional activities when compared to those with the T-106 allele (Z/C-106, 37.4+/-5.4 vs. Z/T-106 7.7+/-1.6, P<0.003; Z-2/C-106, 58.7+/-9.9 vs. Z-2/T-106 10.9+/-0.6, P<0.0001). These results demonstrate that the Z-2/C-106 haplotype is associated with elevated transcriptional activity of the aldose reductase gene. This in turn may explain the role of these polymorphisms in the susceptibility to diabetic microvascular complications.
The catabolism of glucose and xylose was studied in a wild type and creA deleted (carbon catabolite de-repressed) strain of Aspergillus nidulans. Both strains were cultivated in bioreactors with either glucose or xylose as the sole carbon source, or in the presence of both sugars. In the cultivations on single carbon sources, it was demonstrated that xylose acted as a carbon catabolite repressor (xylose cultivations), while the enzymes in the xylose utilisation pathway were also subject to repression in the presence of glucose (glucose cultivations). In the wild type strain growing on the sugar mixture, glucose repression of xylose utilisation was observed; with xylose utilisation occurring only after glucose was depleted. This phenomenon was not seen in the creA deleted strain, where glucose and xylose were catabolised simultaneously. Measurement of key metabolites and the activities of key enzymes in the xylose utilisation pathway revealed that xylose metabolism was occurring in the creA deleted strain, even at high glucose concentrations. Conversely, in the wild type strain, activities of the key enzymes for xylose metabolism increased only when the effects of glucose repression had been relieved. Xylose was both a repressor and an inducer of xylanases at the same time. The creA mutation seemed to have pleiotropic effects on carbohydratases and carbon catabolism.