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At least 19 recordsLinked to original sources
PubMed1984

L-Sorbose metabolism in Klebsiella pneumoniae and Sor+ derivatives of Escherichia coli K-12 and chemotaxis toward sorbose.

L-Sorbose degradation in Klebsiella pneumoniae was shown to follow the pathway L-sorbose leads to L-sorbose-1-phosphate leads to D-glucitol-6-phosphate leads to D-fructose-6-phosphate. Transport and phosphorylation of L-sorbose was catalyzed by membrane-bound enzyme IIsor of the phosphoenolpyruvate-dependent carbohydrate:phosphotransferase system, specific for and regulated by this ketose and different from all other enzymes II described thus far. Two soluble enzymes, an L-sorbose-1-phosphate reductase and a D-glucitol-6-phosphate dehydrogenase, were involved in the conversion of L-sorbose-1-phosphate to D-fructose-6-phosphate. This dehydrogenase was temperature sensitive, preventing growth of wild-type strains of K. pneumoniae at temperatures above 35 degrees C in the presence of L-sorbose. The enzyme was distinct from a second D-glucitol-6-phosphate dehydrogenase involved in the metabolism of D-glucitol. The sor genes were transferred from the chromosome of nonmotile strains of K. pneumoniae by means of a new R'sor+ plasmid to motile strains of Escherichia coli K-12. Such derivatives not only showed the temperature-sensitive Sor+ phenotype characteristic for K. pneumoniae or Sor+ wild-type strains of E. coli, but also reacted positively to sorbose in chemotaxis tests.

Biological Transport↗
PubMed2005

Candida albicans SOU1 encodes a sorbose reductase required for L-sorbose utilization.

Previous work in our laboratory showed that L-sorbose utilization in Candida albicans is subject to a novel form of regulation which involves a reversible increase or decrease in the copy number of chromosome 5. Furthermore, the structural gene SOU1 is required for L-sorbose utilization and encodes a member of the short chain dehydrogenase family. However, the precise function of SOU1 was not known and neither was the pathway for L-sorbose utilization. We have now expressed SOU1 at a high level from a replicative plasmid having a constitutive ADH1 promoter and purified a version of Sou1p tagged with the FLAG epitope at the N-terminus. Sou1FLAGNp has a sorbose reductase activity which utilizes NADPH as a co-factor and converts L-sorbose to D-sorbitol. It can also less efficiently utilize fructose as a substrate with NADPH as a co-factor, converting fructose to mannitol. In agreement with prediction, the purified enzyme has a subunit molecular weight of 31 kDa and a pI of about 4.8. It probably consists of four identical subunits and has a pH optimum of 6.2. The L-sorbose utilization pathway in C. albicans probably converts L-sorbose to fructose-6-phosphate via D-sorbitol as an intermediate. The first step is catalysed by Sou1p. We also found that C. albicans extracts have a D-sorbitol-6-phosphate dehydrogenase activity, not encoded by SOU1, which utilizes NADP as a co-factor. This activity has not been described previously in yeasts and may be involved in the conversion of phosphorylated D-sorbitol to fructose-6-phosphate or glucose-6-phosphate.

Base Sequence↗
PubMed2002

NADPH-dependent L-sorbose reductase is responsible for L-sorbose assimilation in Gluconobacter suboxydans IFO 3291.

The NADPH-dependent L-sorbose reductase (SR) of L-sorbose-producing Gluconobacter suboxydans IFO 3291 contributes to intracellular L-sorbose assimilation. The gene disruptant showed no SR activity and did not assimilate the once-produced L-sorbose, indicating that the SR functions mainly as an L-sorbose-reducing enzyme in vivo and not as a D-sorbitol-oxidizing enzyme.

Carbohydrate Dehydrogenases↗
PubMed1980

Kinetic analysis of simultaneously occurring proton-sorbose symport and passive sorbose transport in Saccharomyces fragilis.

Sorbose transport in Saccharomyces fragilis takes place both via an active sugar-H+ symport system and via facilitated diffusion. To establish whether the two modes of transport proceed via the same transporter or via two different carriers, the kinetic consequences of both models were investigated. The kinetic equations for initial transport were derived for three possible reaction sequences with respect to sugar and H+ binding to the symport carrier: random binding and obligatory ordered binding with either sugar or H+ binding first, yielding six sets of kinetic parameters. Analysis of experimental data of sorbose transport in S. fragilis showed the existence of separate carriers for active, sorbose-H+ symport and facilitated diffusion. Furthermore, it could be concluded that the symport carrier shows random binding of sugar and H+. In recent literature, a similar combination of active and passive sugar transport in Rhodotorula gracilis and Chlorella vulgaris was interpreted as two modes of action of the same carrier, viz., active symport via the protonated, and facilitated diffusion via the unprotonated carrier. Analysis of the experimental data according to the criteria presented in this paper showed, however, that this supposition is untenable and that two different carriers must also be involved in these micro-organisms.

Biological Transport↗
PubMed1991

Steric and electronic effects in the formation of dihexulose dianhydrides. Reaction of racemic sorbose in anhydrous hydrogen fluoride and a facile synthesis of D-sorbose.

Treatment of DL-sorbose with anhydrous hydrogen fluoride gave a high yield of alpha-D-sorbopyranose alpha-L-sorbopyranose 1,2':2,1'-dianhydride. Similarly a mixture of D-fructose and D-sorbose gave a good yield of beta-D-fructopyranose alpha-D-sorbopyranose 1,2':2,1'-dianhydride. The formation of these products compared to the more complicated mixtures of compounds obtained by treatment of L-sorbose or D-fructose with hydrogen fluoride, is discussed in terms of conformations, and steric and electronic factors.

Carbohydrate Conformation↗
PubMed1975

Deoxyfluoroketohexoses: 4-deoxy-4-fluoro-D-sorbose and -tagatose and 5-deoxy-5-fluoro-L-sorbose.

4-Deoxy-4-fluoro-alpha-D-sorbose (6) was prepared in crystalline form by the action of potassium hydrogen fluoride on 3,4-anhydro-1,2-O-isopropylidene-beta-D-psicopyranose (3) followed by deacetonation. Under identical conditions, 3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose (7) underwent epoxide migration to give 4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose (12), which after deacetonation yielded 4-deoxy-4-fluoro-D-tagatose (15) and 5-deoxy-5-fluoro-alpha-L-sorbopyranose (16), the latter as the crystalline, free sugar. The action of glycol-cleavage reagents on the isopropylidene acetals of the deoxyfluoro sugars was consistent with the assigned structures. The structures were established by 13-C n.m.r. studies of the free deoxyfluoro sugars 6 and 16 and of the isopropylidene acetal 13, and by 1-H n.m.r. studies on the acetylated isopropylidene acetals 5 diacetate, 13 diacetate, and 14 diacetate. 5-Deoxy-5-fluoro-L-sorbose (16) was biologically active, producing in mice effects characteristic of deoxyfluorotrioses and of fluoroacetate. 4-Deoxy-4-fluoro-D-tagatose (15) and 4-deoxy-4-fluoro-D-sorbose (6) produced no apparent effects in mice up to a dose of 500mg/kg. The implications of these findings with respect to transport, phosphorylation, and the action of aldolase on ketohexoses are discussed.

Antineoplastic Agents↗
PubMed2000

Productivity enhancement in l-sorbose fermentation using oxygen vector.

Sorbose, an intermediate of Vitamin-C is produced by biological oxidation of sorbitol by Acetobacter suboxydans. The utility of oxygen vector (N-hexadecane) in enhancing the sorbose accumulation and its productivity was examined for sorbitol to sorbose bioconversion process. Shake flask fermentations were conducted using 1% to 6% (v/v) N-hexadecane. Higher sorbose production was observed in shake flask containing 1-4% N-hexadecane as compared to shake flasks without N-hexadecane. A maximum of 82.12 kgm(-)(3) sorbose accumulated in 24 h by the addition of 4% N-hexadecane as against 64.83 kgm(-)(3) sorbose without the addition of N-hexadecane. However, the concentration of sorbose produced in the same time decreased when 5% and 6% N-hexadecane were used. Batch sorbose fermentation conducted using 4% N-hexadecane demonstrated decrease in the process time from 14 h to 12 h. The productivity increased from 14.3 kgm(-)(3) h(-)(1) to 16.7 kgm(-)(3) h(-)(1) when 4% N-hexadecane was used. Fed-batch fermentation using 4% N-hexadecane was over in 20 h with a productivity of 15.9 kgm(-)(3) h(-)(1), and a sorbose accumulation of 311.68 kgm(-)(3) was obtained. The same fed-batch fermentation finished in 25 h when no N-hexadecane was used. A productivity of 12.6 kgm(-)(3) h(-)(1) and a final sorbose accumulation of 316 kgm(-)(3) were obtained. The increase in productivity and lower process time were achieved by the addition of N-hexadecane to the fermentation medium.

Journal Article↗
PubMed1989

Lower fat deposition and energy utilization of growing rats fed diets containing sorbose.

1. Growing rats were fed diets containing graded levels (0, 100, 200 and 300 g/kg diet) of sorbose for 6 weeks. Protein, fat and energy deposition were determined by carcass analysis. 2. The values for growth, serum insulin level, digestible energy (DE), metabolizable energy (ME) and fat and energy deposition declined with the increment of dietary sorbose. 3. The efficiency of protein utilization (protein retained/protein consumed) was hardly affected by dietary sorbose. The DE and ME of sorbose per se was calculated as 14.09 and 12.35 kJ/g respectively. The efficiency of energy utilization (energy retained/ME intake) decreased with the increase of dietary sorbose, although sorbose had an ME. 4. The relative weights of gastro-intestinal tract and liver were positively associated with dietary sorbose level, although the reverse was true for the amount of stomach content, being heavier with higher dietary sorbose. 5. It is suggested that dietary sorbose, as a sweetener as well as a bulky agent, seems to be a suitable sugar for the obese and diabetic with special reference to lower body fat and energy deposition without reducing protein utilization.

Adipose Tissue↗
PubMed1991

Effect of dietary sorbose on lipid metabolism in male and female broilers.

Male and female broilers were given diets (6 males and 6 females per diet) containing varying percentages of sorbose (0, 3, 6, and 9%) and fed for ad libitum access from 28 to 56 days of age. Body weight gain and feed intake were decreased with increasing dietary sorbose, particularly in male birds fed diets containing 9% sorbose, although feed efficiency and N retention rate were not influenced by dietary treatments. Absolute and relative abdominal fat weights were higher in females than in males and decreased with the increasing levels of dietary sorbose in both sexes. Fat content in the pectoral muscle also decreased as dietary sorbose increased. Dietary sorbose did not have significant effects on serum glucose, triglyceride, total cholesterol, low density lipoprotein, very low density lipoprotein, and chylomicron levels in either male or female birds. The ME values of diets decreased as dietary sorbose increased. Palmitic acid content of abdominal fat was significantly lower in birds fed the 9% sorbose diet than in birds fed the control diet. The reverse was true for linoleic acid content. It was concluded that dietary sorbose can be used as a potential regulator of lipid deposition in broilers.

Adipose Tissue↗
PubMed1993

Reduced plasma cholesterol and lipoprotein in laying hens without concomitant reduction of egg cholesterol in response to dietary sorbose.

Experiments were conducted to determine the effect of sorbose on feed consumption, egg production and size, and cholesterol metabolism of laying hens. In Experiment 1, 87-wk-old laying hens (10 per treatment) were fed diets containing 0, 10, or 20% sorbose for 4 wk. In a second experiment, 108-wk-old laying hens (eight per treatment) were fed a control diet, a diet with 10% added sorbose, or the control diet with intake restricted to the level of sorbose-treated hens for 4 wk. Feed consumption and egg production were recorded daily. Plasma and egg cholesterol levels were determined at 0, 2, and 4 wk. Plasma and egg very low density lipoprotein (VLDL) concentrations were determined after 4 wk. Egg production, feed intake, and body weight gain were significantly reduced by dietary sorbose. Egg and yolk weight and percentage yolk decreased in response to sorbose. Sorbose significantly reduced plasma cholesterol and VLDL by approximately 50%, compared with the hens fed a control diet. Egg cholesterol concentration (milligrams per gram of yolk) was significantly increased, although the reduction in yolk size resulted in similar total egg cholesterol (milligrams per egg). Restricting feed intake of laying hens significantly lowered plasma cholesterol, but not to levels comparable to that of sorbose-treated hens. The data indicate that substantial reduction of plasma cholesterol and VLDL by dietary sorbose was not accompanied by reduced egg cholesterol.

Animal Feed↗
PubMed2000

Optimized synthesis of L-sorbose by C(5)-dehydrogenation of D-sorbitol with Gluconobacter oxydans.

The optimization of L-sorbose synthesis by regiospecific dehydrogenation of D-sorbitol using Gluconobacter oxydans is reported. The current L-sorbose production processes that are based on G. oxydans and other bacterial strains are suboptimal as to yield and rate of L-sorbose synthesis. One reason for these problems is the toxicity that is induced by the substrate D-sorbitol when used in concentrations of >10% (w/v). This phenomenon significantly limits the potentials of L-sorbose production from an industrial point of view. The goal of this study was to develop a fast production process that yields L-sorbose in stoichiometric amounts starting from D-sorbitol concentrations that exceed 10% (w/v). A gradual improvement of the inoculum build-up procedure, culture medium composition, and process parameters ultimately led to a theoretically maximal L-sorbose productivity (200 g L(-1) of L-sorbose from 200 g L(-1) of D-sorbitol in 28 h of fermentation) using a Gluconobacter oxydans mutant strain that was selected under conditions of substrate inhibition. Because the D-sorbitol/L‐sorbose bioconversion is used to mass-produce vitamin C, the procedure reported here will contribute to a more efficient and more economic synthesis of vitamin C.

Ascorbic Acid↗