THE USE OF PYROPHOSPHATE BUFFER FOR THE MANOMETRIC ASSAY OF XANTHINE OXIDASE

Single substrate-functionalized molybdenum oxide nanozyme for specific colorimetric monitoring of xanthine oxidase activity

Xanthine-functionalized molybdenum oxide nanodots (X-MoO3-x NDs) with peroxidase (POD)-like activity were developed for selective, sensitive, and facile colorimetric quantification of xanthine oxidase (XO). Xanthine functionalization can not only be favorable for the successful nanozyme preparation, but also for the specific recognition of XO as well as the simultaneous generation of hydrogen peroxide, which was subsequently transformed into hydroxyl radical to oxidize the chromogenic reagent based on the POD-like catalysis. Under the optimized conditions, the colorimetric biosensing platform was established for XO assay without addition of further substrates, showing good linearity relationship between absorbance difference (ΔA) and XO concentrations in the range 0.05-0.5 U/mL (R2 = 0.998) with a limit of detection (LOD) of 0.019 U/mL. The quantification of XO occurs in 25 min, which is superior to the previously reported and commercial XO assays. The proposed method has been successfully used in the assay of human serum samples, showing its high potential in the field of clinical monitoring.

MOF based fluorescent assay of xanthine oxidase for rapid inhibitor screening with real-time kinetics monitoring

The activity assay of xanthine oxidase (XO) is of great application value in clinical diagnosis because the abnormal level of this enzyme is related to a series of pathological states. In this work, a Zr based metal-organic framework (BTB-MOF) with stable photoluminescence in pure water and buffer solution was synthesized. The examination about the fluorescent responses of this material to xanthine and its oxidation product, uric acid, showed that, although both of them affected the emission of BTB-MOF in quenching form, the efficiencies presented much difference. Taking advantage of this feature, a fluorescent method was developed for the activity assay of XO, that is, BTB-MOF was added to the enzymatic oxidation system as a sensor to transduce the proceeding of the reaction real-timely to the signal of fluorescent intensity change. Our method can work under the interference of normal biologically related species, and precisely reflect XO activity in the range of 0.2-40 U L^-1 (detection limit = 0.004 U L^-1). With consecutive fluorescence intensity scan, this assay could be applied as a high speed screening method of XO inhibitors with the testing time of 1 min. This work shows the wide potential application of MOFs in enzyme analysis.

Inhibition of enzymes by alkylsalicylic acids

5-n-Alkylsalicylates inhibited a variety of enzymes that transform acidic substances, viz. glucose-6-phosphate dehydrogenase, glyoxalase, xanthine oxidase, carbonic anhydrase and D-amino-acid oxidase. Inhibitory potency rose to a peak at the n-nonyl derivative. None of the tests were of value, either singly or in combination, as screening processes for anti-inflammatory activity. The comparable results with a trinitrobenzaldehyde reagent suggest that the various inhibitions arise by non-specific association of the drugs with arginine and lysine residues in proteins.

Protein deficiency in spaced-fed rats

1. Adult rats were trained to consume the entire day's ration in 2 h. They showed marked difference in food intake when a diet lacking in protein was given. Two broad stages were observed, the first phase did not show any drop in calorie intake whereas the second showed distinct severe calorie deficiency.

2. Definite changes were noted in the metabolic profiles of the protein-deficient group even though no evidence for a fall in calorie intake (stage 1) was provided by the measurements of body and organ weights, urinary end-products, liver constituents and liver enzymes.

3. The levels of urinary end-products and liver DNA and RNA decreased in the proteindeficient and pair-fed control groups compared with the control group.

4. The liver glycogen content remained unchanged in the protein-deficient groups whereas the lipid content and the ratio of vitamin A alcohol to ester increased significantly.

5. The activity of xanthine oxidase in the liver was reduced by 75% in the pair-fed control group and by 95% in the protein-deficient group when compared with the control group. However, the activity of succinic dehydrogenase varied, depending on the unit of activity used to express it.