- Xylose isomerase (XI) (from gut Bacteroidetes cluster, e.g., Bacteroides thetaiotaomicron and Bacteroides ovatus): Catalyzes conversion of Xylose to xylulose [2]
- Xylose kinase (XK) (endogenous in recombinant yeast): Catalyzes phosphorylation of xylulose (product of Xylose isomerization) to xylulose-5-phosphate [2,3]

- 2,3-Butanediol production: When Xylose (50 g/L) was used as the sole carbon source in bacterial fermentation, simultaneous addition of yeast extract (5 g/L), Na₂EDTA (0.5 mM), and acetic acid (2 g/L) increased 2,3-butanediol yield by 42% compared to the control group (without additives). The final 2,3-butanediol concentration reached 22.8 g/L, with a Xylose utilization rate of 91% [1]
- Ethanol production by recombinant yeast: Recombinant Saccharomyces cerevisiae expressing gut Bacteroidetes XI (e.g., from Bacteroides thetaiotaomicron) utilized Xylose (40 g/L) for ethanol fermentation. After 72 h of culture, the ethanol yield was 0.42 g/g Xylose, which was 35% higher than that of yeast expressing fungal XI. The Xylose consumption rate was 0.58 g/(L·h) [2]
- Industrial enzyme production by recombinant yeast: Recombinant Pichia pastoris harboring enzyme-encoding genes (e.g., cellulase) utilized Xylose (30 g/L) as a carbon source. After 96 h of induction, the enzyme activity in the culture supernatant was 18.5 U/mL, with a Xylose utilization rate of 87%. This was comparable to glucose-based culture (enzyme activity: 19.2 U/mL) [3]

- Xylose isomerase (XI) activity assay: The reaction system (1 mL) contained 50 mM Tris-HCl buffer (pH 7.5), 10 mM MgCl₂, 50 mM Xylose (substrate), and 10 μL recombinant XI enzyme solution. The reaction was incubated at 37°C for 60 min, then terminated by boiling for 5 min. The amount of xylulose (product of Xylose isomerization) was detected by high-performance liquid chromatography (HPLC) with a refractive index detector. XI activity was defined as the amount of enzyme that produces 1 μmol xylulose per minute [2]

- Bacterial fermentation for 2,3-butanediol production: The fermentation medium contained Xylose (50 g/L), (NH₄)₂SO₄ (2 g/L), KH₂PO₄ (1.5 g/L), MgSO₄·7H₂O (0.5 g/L), plus yeast extract (5 g/L), Na₂EDTA (0.5 mM), and acetic acid (2 g/L) as additives. The medium was inoculated with bacterial culture (10% v/v, OD₆₀₀ = 1.0) and incubated at 30°C with shaking at 200 rpm for 48 h. Samples were taken every 12 h, centrifuged at 8000 × g for 10 min, and the supernatant was analyzed by HPLC to determine Xylose concentration and 2,3-butanediol yield [1]
- Recombinant Saccharomyces cerevisiae fermentation for ethanol production: Yeast cells were pre-cultured in YPD medium (yeast extract, peptone, glucose) to OD₆₀₀ = 2.0, then inoculated into YPX medium (yeast extract, peptone, 40 g/L Xylose) at 5% v/v. The culture was incubated at 30°C with shaking at 150 rpm for 72 h. Ethanol concentration was measured by gas chromatography, and Xylose concentration was determined by HPLC [2]
- Recombinant Pichia pastoris culture for enzyme production: The seed medium contained Xylose (20 g/L), yeast extract (10 g/L), and peptone (20 g/L). The cells were cultured at 30°C with shaking at 220 rpm for 24 h, then transferred to the production medium (30 g/L Xylose, 5 g/L yeast extract, 10 g/L peptone) at 10% v/v. After 96 h of induction at 28°C, the culture was centrifuged at 6000 × g for 15 min, and the supernatant was collected to measure enzyme activity via colorimetric assay [3]

Absorption, Distribution and Excretion
When 12 healthy subjects received 10 g of D-xylose intravenously, followed by 25 g orally one week later, the observed absorption rate was approximately 69.4% (p < 0.002), and the observed absorption rate was approximately 1.03 mg/h (p < 0.05). The maximum concentration observed in the subjects was 0.53 mg/L, and the time to reach maximum concentration was 71 minutes. The recorded absolute bioavailability was 69%. In patients with normal renal function, renal excretion accounted for approximately half (50%) of the total D-xylose clearance. Any D-xylose clearance via non-renal routes was considered hepatic clearance. The volume of distribution of D-xylose in normal healthy subjects was 0.22 L/kg. The renal clearance in healthy individuals was 89 ml/min. The associated plasma clearance and non-renal clearance were 180 and 91 ml/min, respectively. Xylose has been shown to enter the aqueous humor of rats from systemic circulation, thereby reaching the lens.
Absorption via the gastrointestinal tract…5 g dose is absorbed more rapidly and completely than 25 g dose…at least 60%…absorbed in the proximal small intestine…independent of the presence of bile or pancreatic juice…peak plasma concentration is reached after 1 to 2 hours…decreases to 0 after 5 hours (human, oral 5 g or 25 g).
Plasma half-life…approximately 1 hour HR/IV dosing/…approximately 60%…metabolized to carbon dioxide and water, D-threitol and…unidentified metabolites…excreted in urine…approximately 25% of 25 g/dose and approximately 35% of 5 g/dose are excreted unchanged in urine within 5 hours (human, oral).
Urinary excretion/primarily via/glomerular filtration…a small amount of renal tubular reabsorption may occur (human, oral).
For more complete data on absorption, distribution, and excretion of (D)-xylose (8 in total), please visit the HSDB record page.
Metabolism/Metabolites
The most common and traditional metabolic pathway for xylose is the oxidoreductase pathway (or xylose reductase-xylitol dehydrogenase pathway, XR-XDH pathway). In this pathway, xylose is first reduced to xylitol by xylitol dehydrogenase (XDH) under the action of NADH or NADPH. The resulting xylitol is then oxidized to D-xylitol by xylitol dehydrogenase (XDH) under the action of the cofactor NAD. Finally, D-xylitol is phosphorylated by an ATP-utilizing kinase (xylitol kinase) to produce D-xylitol-5-phosphate, which is an intermediate in the pentose phosphate pathway of nucleotide synthesis.
...Rat liver microsomes catalyze...the transfer of xylitol from...UDP-xylitol to bilirubin...
Approximately 60% of absorbed xylitol is metabolized to carbon dioxide, water, D-threitol, and other unidentified metabolites (human, oral).
After intraperitoneal injection of 14C-labeled D-xylulose into guinea pigs, 10.8 g of radioactive material was recovered within 4 hours, present as exhaled carbon dioxide. 41.3 mg (expressed as 14C) was detected in urine within 5 hours. Approximately 60 mg of the radioactive material in urine was D-xylose.
In intact animals, as well as in vitro, the kidneys and liver can oxidize 14C-labeled D-xylose to labeled carbon dioxide. The oxidation of D-xylose in guinea pigs likely involves its initial conversion to D-xylose followed by decarboxylation.
In vitro, the kidneys and liver can oxidize D-xylose to carbon dioxide. Liver extracts can catalyze its conversion to D-xylose with pyridine nucleotides as a cofactor. This enzyme activity differs from that of hepatic glucose dehydrogenase.
Biological Half-Life
The elimination half-life observed in healthy individuals was 75 minutes.

Protein Binding
Currently, there is no readily available data on the protein binding of xylose in the human body. Interactions D-xylose can alleviate the inhibitory effects of puromycin and cyclohexylimide on the incorporation of chondroitin sulfate into the tibia and femur of embryonic chickens. Adding guar gum during oral administration of D-xylose in volunteers slows its gastrointestinal absorption. Total absorption and plasma half-life of D-xylose were not affected. Concomitant administration of indomethacin, neomycin, phenformin, colchicine, or high doses of aminosalicylic acid inhibits intestinal absorption of D-xylose, thereby reducing sugar excretion… Aspirin reduces urinary excretion of D-xylose, possibly by altering renal function. Non-human Toxicity Oral LD50 in mice: 23 g/kg Intravenous LD50 in mice: 11,300 mg/kg

[1]. The implementation of high fermentative 2,3-butanediol production from xylose by simultaneous additions of yeast extract, Na2EDTA, and acetic acid. N Biotechnol. 2015 Aug 3.

[2]. Bacterial xylose isomerases from the mammal gut Bacteroidetes cluster function in Saccharomyces cerevisiae for effective xylose fermentation. Microbial Cell Factories May, 2015, 14:70.

[3]. Construction of efficient xylose utilizing Pichia pastoris for industrial enzyme production. Microbial Cell Factories February 2015, 14:22.

D-xylopyranose is the pyranose form of D-xylose. Xylose is an aldose monosaccharide composed of five carbon atoms and one aldehyde group. Xylose is a sugar extracted from wood. D-xylose is a widely used diabetic sweetener in food and beverages. Xylose has also been used as a diagnostic reagent to observe malabsorption. Xylose can be catalytically hydrogenated to produce xylitol [DB11195], a common food additive sweetener substitute. Dextrorotatory xylose (D-xylose) usually refers to the endogenous form of xylose in organisms. Levorotatory xylose (L-xylose) refers to the synthetic form of xylose. However, xylose itself may not have many direct uses, but its metabolites provide a variety of important nutritional and biological functions. D-xylose is a metabolite found or produced in Escherichia coli (K12 strain, MG1655 strain). D-xylose has also been reported in apple plants, Eliodia paniculata, and other organisms with relevant data. Xylose, also known as xylose sugar, is an aldose—a monosaccharide containing five carbon atoms and one aldehyde group. Its chemical formula is C5H10O5, and its sweetness is about 40% that of sucrose. Xylose is found in the germ of most edible plants. Xylan, a polysaccharide tightly bound to cellulose, is almost entirely composed of D-xylose. It is abundant in corn cobs, cottonseed hulls, pecan shells, and rice straw. Xylose is also found in mucopolysaccharides in connective tissues and sometimes in urine. In the O-glycosylation of proteoglycans, xylose is the first sugar added to a serine or threonine residue. Therefore, xylose participates in the biosynthetic pathways of most anionic polysaccharides, such as heparan sulfate and chondroitin sulfate. Medically, xylose is used to detect malabsorption by administering a xylose solution to a patient after fasting. If xylose is detected in the blood and/or urine over the next few hours, it indicates that xylose has been absorbed by the intestines. Xylose is considered one of the eight essential sugars for the human body. The other eight are galactose, glucose, mannose, N-acetylglucosamine, N-acetylglucosamine, fucose, and sialic acid. (Wikipedia)

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Drug Indications
The main use of xylose in daily nutrition is as a parent sugar alcohol, from which another sugar alcohol—xylitol—can be derived. Xylitol is an extremely common food additive or sweetener that can replace regular sugar, providing a lower-calorie sweetness. In addition, xylose is used in a procedure called the D-xylose absorption test, which was previously used to assess an individual's ability to absorb monosaccharides such as D-xylose from the intestines. This test determines whether nutrients are properly absorbed in the patient's gastrointestinal tract by measuring the D-xylose content in urine and blood samples after the subject ingests a certain amount of water-soluble D-xylose.

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Mechanism of Action
Xylose is metabolized into a variety of chemical intermediates, which play a key role in human biological homeostasis. In eukaryotes, xylose is ultimately metabolized to (D)-xylulose-5-phosphate via an oxidoreductase metabolic pathway, which is an intermediate in the pentose phosphate pathway. In the pentose phosphate pathway, NADPH, pentose pentose, and ribose-5-phosphate serve as raw materials and precursors for nucleotide synthesis. In particular, xylulose-5-phosphate can be directly used for the generation of glyceraldehyde-3-phosphate in this pathway. Other studies have also suggested that xylulose-5-phosphate may play a role in gene expression, perhaps by promoting the ChREBP transcription factor under nutrient-adequate conditions.

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Therapeutic Uses
Measurement of blood xylone levels…used to determine whether abnormally low urinary xylone excretion is due to malabsorption or renal insufficiency. Blood xylose level/measurement/2 hours after administration of a 25 g dose.
/differentiation/steatorrhea due to pancreatic insufficiency versus steatorrhea due to malabsorption/5 g dissolved in 150 ml of water or 25 g dissolved in 250 ml of water, followed by oral administration of 250 ml of water. Collect urine and determine xylose levels within the next 5 hours.
Assess intestinal absorption…Diagnose malabsorption due to intestinal mucosal disease/Dissolve 5g in 150ml of water, or 25g in 250ml of water, then orally administer 250ml of water. Collect urine and determine xylose levels within the next 5 hours.
Diagnose malabsorption due to… /Assess/ the degree of malabsorption or treatment response/5g dissolved in 250ml of water orally. Fluid supplementation is permitted. Collect urine at 2 and 3 consecutive hours. Determine xylose levels/.
For incontinent infants, young children, or elderly patients…Intestinal absorption can be assessed using xylose blood concentrations/500mg/kg body weight (or a maximum dose of 25g), orally in a 5-10% aqueous solution. Xylose levels are determined by collecting blood samples at 30 minutes, 1 hour, and 2 hours after xylose administration.

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Drug Warnings
In patients over 60 years of age, xylose urinary excretion is typically low…Xylose testing should only be used in pregnant women or women who may become pregnant if the potential benefits outweigh the possible risks.
Situations that may lead to false-positive test results include: vomiting, gastric retention, thyroid dysfunction, and severe diarrhea following administration of the test dose.
In patients with thyrotoxicosis, urinary xylose excretion is increased.
Using xylose testing requires close attention to technical details…Patients with impaired renal function, dehydration, insufficient circulating blood volume, edema, or significant ascites may have lower than normal urinary D-xylose excretion, leading to false-positive test results.

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Pharmacodynamics
Xylose is commonly used as a parent sugar alcohol; xylose hydrogenation yields xylitol, a commonly used food additive sweetener. Xylitol possesses many properties that make it a healthy and effective alternative to common sugars.
For example, while xylitol looks and tastes exactly like regular sugar, and its sweetness is comparable to that of regular sucrose (100%), it has very little effect on blood sugar and insulin secretion, and contains only 2.4 calories per gram. Furthermore, xylitol is non-fermentable and therefore not converted into acid by oral bacteria, thus helping to maintain the pH balance in the mouth. Multiple studies have shown that it is precisely because of this property that xylitol products (such as chewing gum) are effective in reducing tooth decay. In summary, these properties make xylose and its metabolite xylitol an ideal choice for diabetics or those who wish to maintain a healthy diet, serving as an effective alternative to sweeteners in healthy foods.

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- Background: Xylose is the most abundant pentose in nature, primarily derived from the hydrolysis of plant hemicellulose (such as corn stalks and bagasse). Xylose is a key renewable carbon source for microbial fermentation to produce biofuels (such as ethanol) and high-value chemicals (such as 2,3-butanediol) [1,2,3]. Metabolic Mechanism: In recombinant microorganisms (e.g., yeast), xylose is first isomerized to xylulose by xylose isomerase, and then phosphorylated to xylulose-5-phosphate by xylose kinase. Xylulose-5-phosphate further enters the pentose phosphate pathway for energy metabolism or biosynthesis of target products [2,3]. Application Significance: The efficient utilization of xylose by microorganisms can broaden the range of renewable raw materials for industrial fermentation, reduce the production costs of biofuels and industrial enzymes, and promote the development of bio-based industries [1,3].

C5H10O5

150.1299

150.052

58-86-6

135191

Monoclinic needles or prisms
White crystalline powder

1.5±0.1 g/cm3

415.5±38.0 °C at 760 mmHg

148-158 ºC

219.2±23.3 °C

0.0±2.2 mmHg at 25°C

1.544

-2.39

4

5

0

10

117

3

O([H])[C@]([H])([C@]([H])(C([H])=O)O[H])[C@@]([H])(C([H])([H])O[H])O[H]

SRBFZHDQGSBBOR-IOVATXLUSA-N

InChI=1S/C5H10O5/c6-2-1-10-5(9)4(8)3(2)7/h2-9H,1H2/t2-,3+,4-,5?/m1/s1

(3R,4S,5R)-oxane-2,3,4,5-tetrol

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~50 mg/mL (~333.04 mM)
H2O : ≥ 50 mg/mL (~333.04 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (16.65 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (16.65 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (16.65 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 100 mg/mL (666.09 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)