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At least 73 records · Page 4Linked to original sources
PubMed1987

Mapping of the sor genes for L-sorbose degradation in the chromosome of Klebsiella pneumoniae.

A series of mutants was isolated in Klebsiella pneumoniae strain 1033, among them mutants unable to grow on L-sorbose. Different R' plasmids carrying the sor genes and other surrounding chromosomal genes were also isolated. Each plasmid contained the structural genes sorA for an Enzyme II of the phosphoenolpyruvate-dependent carbohydrate:phosphotransferase system, sorD for a D-glucitol 6-phosphate dehydrogenase, sorE for an L-sorbose 1-phosphate reductase, and the corresponding regulator gene sorR. These structural genes are coordinately expressed and inducible by L-sorbose. Cis-dominant and pleiotropic mutations rendering the expression of the sor genes constitutive or eliminating it were isolated. Complementation of a series of mutations in Escherichia coli K12 and K. pneumoniae by various R' and F' plasmids and by P1 transduction in K. pneumoniae located the sor genes within the following gene sequence: rbs rha pfkA metB ppc argH ilv btuB rpoB metA ace sor pgi malB uvrA. The rbs-ilv gene loci tightly linked in E. coli K12 at 84 min, are separated in the map of K. pneumoniae 1033 and located at 86 and 89 min, respectively.

Chromosome Mapping↗
PubMed1978

Inhibition of glycolysis by L-sorbose in dog erythrocytes.

We have demonstrated previously that in vitro L-sorbose acts directly on dog erythrocytes to induce hemolysis. Here we report that L-sorbose depresses lactate formation in dog hemolysates from glucose, mannose and fructose but not from glucose-6-phosphate and galactose, suggesting that L-sorbose interacts with glycolysis at the level of the hexokinase.

Animals↗
PubMed1977

Active transport of L-sorbose and 2-deoxy-D-galactose in Saccharomyces fragilis.

Sorbose and 2-deoxy-D-galactose are taken up in Saccharomyces fragilis by an active transport mechanism, as indicated by the energy requirement of the process and the accumulation of free sugar against the concentration gradient. There are no indications for transport-associated phosphorylation as mechanism of energy coupling with these two sugars. The measured sugar-proton cotransport and the influx inhibition by uncouplers suggest a chemiosmotic coupling mechanism. Thus there are at least two different active transport mechanisms operative in Saccharomyces fragilis: transport-associated phosphorylation in the case of 2-deoxy-D-glucose and chemiosmotic coupling in the case of sorbose and 2-deoxy-D-galactose. The differences between the two mechanisms are discussed. Uncouplers do not stimulate downhill sorbose transport in energy-depleted cells and evoke an almost complete inhibition of efflux and of exchange transport. The differences between this sugar-proton cotransport system and similar systems in bacteria and Chlorella are discussed.

Adenosine Triphosphate↗
PubMed1976

Surface tension activity and paramorphogenic effect of sorbose, sodium desoxycholate, and griseofulvin on the growth of colonies of Chaetomium aureum Chivers.

Sorbose at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0% levels, sodium-desoxycholate at 0.025, 0.050, 0.075, 0.1 and 0.125% levels, and griseofulvin at 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, and 0.010% levels restrict the growth of colonies of Chaetomium aureum, both at pH 6.5 and 7.0. Restriction of colonies was most effective with 0.7% sorbose, 0.1% sodium-desoxycholate, and 0.006% griseofulvin in the medium adjusted to pH 6.5. Surface tension activity of sorbose, sodium-desoxycholate, and griseofulvin in different concentrations was determined, following the usual standard method.

Ascomycota↗
PubMed2005

Loss and gain of chromosome 5 controls growth of Candida albicans on sorbose due to dispersed redundant negative regulators.

A reversible decrease or increase of Candida albicans chromosome copy number was found to be a prevalent means of survival of this opportunistic pathogen, under conditions that kill cells or inhibit their propagation. The utilization of a secondary carbon source, l-sorbose, by reversible loss of chromosome 5, serves as a model system. We have determined that an approximately 209-kbp portion of the right arm of chromosome 5 contains at least five spatially separated, functionally redundant regions that control utilization of l-sorbose. The regions bear no structural similarity among themselves, and four of them contain sequences that bear no similarity with any known sequence. We identified a regulatory gene in region A that encodes a helix-loop-helix protein. Most important, the multiple redundant regulators scattered along chromosome 5 explain, in a simple, elegant way, why the loss of the entire homologue is usually required for growth on sorbose. Thus, an entire chromosome acts as a single regulatory unit, a feature not previously considered. Our finding appears to be a paradigm for the control of other phenotypes in C. albicans that also depend on chromosome loss, thus implying that C. albicans genes are not distributed randomly among different chromosomes.

Amino Acid Sequence↗
PubMed1999

Appearance and properties of L-sorbose-utilizing mutants of Candida albicans obtained on a selective plate.

This is the first report that adaptive mutagenesis can arise by chromosomal nondisjunction, a phenomenon previously associated exclusively with DNA alterations. We previously uncovered a novel regulatory mechanism in Candida albicans in which the assimilation of an alternative sugar, l-sorbose, was determined by copy number of chromosome 5, such that monosomic strains utilized l-sorbose, whereas disomic strains did not. We present evidence that this formation of monosomy of chromosome 5, which is apparently a result of nondisjunction, appeared with increased frequencies after a selective condition was applied, i.e., by adaptive mutagenesis. The rate of formation of l-sorbose-utilizing mutants per viable cell per day ranged from 10(-6) at the initial time of detection to 10(-2) after 4 days of incubation on the selective plate.

Candida albicans↗
PubMed1976

Studies on cyclodextrin glycosyltransferase. IV. Enzymatic synthesis of 3-O-alpha-D-glucopyranosyl-L-sorbose and 4-O-alpha-D-glucopyranosyl-D-xylose using cyclodextrin glycosyltransferase.

The acceptor specificity of the transglycosylation reaction of cyclodextrin glycosyltransferase[EC 2.4.1.19] was investigated using various sugars and sugar alcohols. L-Sorbose, D-xylose, and D-galactose, which contain configurational or structural changes relative to the D-glucopyranose unit at positions other than position 1, were also shown to be efficient acceptors in the transglycosylation reaction of this enzyme. It was shown by chemical and enzymatic methods that this enzyme could transfer glycosyl residues only to the C3-hydroxyl group of L-sorbose and C4-hydroxyl group of D-xylose, producing oligosaccharides terminated by 3-O-alpha-D-glucopyranosyl-L-sorbose and 4-O-alpha-D-glucopyranosyl-D-xylose at the reducing ends, respectively.

Acetates↗
PubMed2005

Microbial production of L-ascorbic acid from D-sorbitol, L-sorbose, L-gulose, and L-sorbosone by Ketogulonicigenium vulgare DSM 4025.

Ketogulonicigenium vulgare DSM 4025, known as a 2-keto-L-gulonic acid producing strain from L-sorbose via L-sorbosone, surprisingly produced L-ascorbic acid from D-sorbitol, L-sorbose, L-gulose, and L-sorbosone as the substrate under a growing or resting condition. As the best result, K. vulgare DSM 4025 produced 1.37 g per liter of L-AA from 5.00 g per liter of L-sorbosone during 4 h incubation time at 30 degrees C under the resting cell condition having 5.70 g per liter of wet cells. The precursor of L-AA formation from D-sorbitol and L-sorbose, except for L-gulose, was thought to be the putative furanose form of L-sorbosone. This is the first time it is reported that bacteria can produce vitamin C via L-sorbosone.

Ascorbic Acid↗
PubMed1978

[The influence of non-metabolizable alpha- and beta-glycosides on the regulation of sorbose fermentation of salmonellae (author's transl)].

Fermentation of sorbose by late positive Salmonella wildtype cultures and by mutant strains splitting this sugar promptly is restrained by the beta-glucoside salicine and likewise by 1-o-methyl-alpha-D-glucopyranoside (MGP), but is not influenced by lactose or sucrose. In growing cultures salicine works more powerful on sorbose utilization than MGP while in dense suspensions of non-multiplying bacteria the relations are reversed. Among the majority of wildtype strains this suppressive effect is diminished or abolished by dimethylsulfoxide (DMSO), but there are strains in which the glucoside effect is enhanced by DMSO. The sorbose fermentation lag in the presence of salicine or MGP is detectable, too, in dense suspensions of promptly splitting Salmonella mutant strains in media poorly supplied with nitrogen and must therefore be attributed to a non-mutative event. From prior work (Stenzel, 1977c) we got some evidence that this event might depend on an inhibition of enzyme induction. Targets and mode of action of the alpha- and beta-glucoside largely seem to be identical, though possibly there might exist minor differences.

Benzyl Alcohols↗
PubMed1993

Cloning and restriction mapping of the L-sorbose utilization genes from a clinical isolate of Escherichia coli (1).

About 30% of clinical isolates of Escherichia coli tested utilized L-sorbose as a carbon and energy source. Escherichia coli K-12 is naturally sorbose negative. The genes for L-sorbose utilization (sor+) is being used as a prototype for studying variable genes amongst bacterial pathogens. The sor+ genes from seven isolates were transferable to E. coli K-12. The (sor+) region was cloned into plasmid pBR322 to give pDOK1. Plasmid pDOK1 is approximately 20kb in size. A restriction endonuclease map of pDOK1 is presented.

Cloning, Molecular↗
PubMed2004

A novel enzymatic approach to the massproduction of L-galactose from L-sorbose.

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 Mn(2+), 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 (13)C nuclear magnetic resonance ((13)C NMR) and IR spectra.

Journal Article↗
PubMed2001

Enzymatic synthesis of novel oligosaccharides from L-sorbose, maltose, and sucrose using kojibiose phosphorylase.

Glucosyl-L-sorbose, -maltose, and -sucrose were synthesized using kojibiose phosphorylase (KPase) from Thermoanaerobacter brockii ATCC35047 with beta-D-glucose-1-phosphate (beta-G1P) as a glucosyl donor. One disaccharide and two trisaccharides thus synthesized were isolated by Toyopearl HW-40S column chromatography. The results of KPase digestion, methylation analysis, and 13C-NMR studies indicated that these oligosaccharides were alpha-D-glucopyranosyl-(1-->5)-alpha-L-sorbopyranose, alpha-D-glucopyranosyl-(1-->2)-alpha-D-glucopyranosyl-(1-->4)-D-glucopyranose (4-alpha-D-kojibiosyl-glucose), and alpha-D-glucopyranosyl-(1-->2)-alpha-D-glucopyranosyl-(1-->2)-beta-D-fructofuranoside, which are all novel oligosaccharides. Glucosyl-L-sorbose was partially hydrolyzed to glucose and L-sorbose by alpha-glucosidases, while glucosyl-sucrose and glucosyl-maltose were not hydrolyzed by glucoamylase, alpha-glucosidases, or CGTase.

Journal Article↗
PubMed1975

Stimulation by organic solvents and detergents of conversion of L-sorbose to L-sorbosone by Gluconobacter melanogenus IFO 3293.

Treatment of Gluconobacter melanogenus IFO 3293 cells with benzene, carbon tetrachloride, cyclohexane, deoxycholate, toluene, or xylene stimulated their conversion of L-sorbose to L-sorbosone two- to threefold. The degree of stimulation depended upon the length of exposure time to the agent and the age of the G. melanogenus cells. A rapid decrease in viability of the cells and degradation of cell RNA was noted after treatment with the effective agents. The G. melanogenus cells were unable to absorb L-sorbose actively after toluene treatment.

Age Factors↗
PubMed1990

Positive and negative regulation of expression of the L-sorbose (sor) operon by SorC in Klebsiella pneumoniae.

In Klebsiella pneumoniae the gene products involved in the degradation of the ketose L-sorbose are encoded in the sor operon. It comprises, besides structural genes for uptake and catabolism, a promoter-proximal gene sorC, encoding a protein SorC of Mr 40 kDa, for which no enzymatic function has been detected. All sor genes are coordinately expressed and inducible by L-sorbose. Polar insertions and frameshift mutations in sorC cause a pleiotropic negative effect on the expression of all other sor genes. This defect is complemented in trans by the wild-type sorC+ allele for frameshift mutations, but not for polar insertions. A single promoter for all sor genes, for which SorC is the activator, thus seems to be located in front of sorC. The repressor activity of SorC was demonstrated by complementation of constitutive sorC alleles with a sorC+ allele leading to inducible expression of all sor genes, including sorC, which, as visualized by the use of a series of lacZ fusions, thus autoregulates its expression, both as an activator and a repressor.

Bacterial Proteins↗
PubMed1994

Sequence of the sor-operon for L-sorbose utilization from Klebsiella pneumoniae KAY2026.

We have sequenced the complete sor-operon of Klebsiella pneumoniae KAY2026. The operon has been mapped at 91 min on the Klebsiella gene-map. It comprises seven open reading frames for the genes sorCDFBAME, which are expressed from the single promotor sorCP. The gene sorC codes for a regulator protein that positively and negatively regulates the expression of the operon; sorD encodes a D-glucitol-6-phosphate dehydrogenase, the genes sorFBAM encode four proteins of a phosphoenolpyruvate-dependent L-sorbose-phosphotransferase system and sorE, finally, an L-sorbose-1-phosphate-reductase.

Amino Acid Sequence↗
PubMed2001

Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.

Catalysis↗
PubMed2003

Attenuated total reflectance Fourier transform mid-infrared spectroscopic quantification of sorbitol and sorbose during a Gluconobacter biotransformation process.

Mid-infrared spectroscopy (MIRS) was used to simultaneously detect and predict concentrations of D-sorbitol and L-sorbose during a Gluconobacter suboxydans biotransformation. Quantitative models for both these compounds were developed for the entire time-course of the process and validated externally using samples not included in the original modelling exercise, giving standard errors of prediction of 3.29 and 3.3% for sorbitol and sorbose, respectively, and a correlation coefficient close to 1.

Bioreactors↗
PubMed1998

Monosomy of a specific chromosome determines L-sorbose utilization: a novel regulatory mechanism in Candida albicans.

We report the identification of the gene, SOU1, required for L-sorbose assimilation in Candida albicans. The level of the expression of SOU1 is determined by the copy number of chromosome III (also denoted chromosome 5), such that monosomic strains assimilate L-sorbose, whereas disomic strains do not, in spite of the fact that SOU1 is not on this chromosome. We suggest that C. albicans contains a resource of potentially beneficial genes that are activated by changes in chromosome number, and that this elaborate mechanism regulates the utilization of food supplies and possibly other important functions, thus representing a novel general means for regulating gene expression in microbes.

Alcohol Oxidoreductases↗