Quantitative characterization of the compensating effects of trimethylamine-N-oxide and guanidine hydrochloride on the dissociation of human cyanmethmoglobin

Simultaneous quantification of trimethylamine N-oxide, trimethylamine, choline, betaine, creatinine, and propionyl-, acetyl-, and L-carnitine in clinical and food samples using HILIC-LC-MS

Trimethylamine-N-oxide (TMAO), a microbiome-derived metabolite from the metabolism of choline, betaine, and carnitines, is associated to adverse cardiovascular outcomes. A method suitable for routine quantification of TMAO and its precursors (trimethylamine (TMA), choline, betaine, creatinine, and propionyl-, acetyl-, and l-carnitine) in clinical and food samples has been developed based on LC-MS. TMA was successfully derivatized using iodoacetonitrile, and no cross-reactions with TMAO or the other methylamines were detected. Extraction from clinical samples (plasma and urine) was performed after protein precipitation using acetonitrile:methanol. For food samples (meatballs and eggs), water extraction was shown to be sufficient, but acid hydrolysis was required to release bound choline before extraction. Baseline separation of the methylamines was achieved using a neutral HILIC column and a mobile phase consisting of 25 mmol/L ammonium formate in water:ACN (30:70). Quantification was performed by MS using external calibration and isotopic labelled internal standards. The assay proved suitable for both clinical and food samples and was linear from ≈ 0.1 up to 200 μmol/L for all methylamines except for TMA and TMAO, which were linear up to 100 μmol/L. Recoveries were 91–107% in clinical samples and 76–98% in food samples. The interday (n=8, four duplicate analysis) CVs were below 9% for all metabolites in clinical and food samples. The method was applied successfully to determine the methylamine concentrations in plasma and urine from the subjects participating in an intervention trial (n=10) to determine the effect of animal food ingestion on methylamine concentrations.

Quantitative characterization of nonspecific self- and hetero-interactions of proteins in nonideal solutions via static light scattering

The dependence of static light scattering upon the compositions of solutions including hen egg white ovalbumin, hen egg white ovomucoid, ribonuclease A, and binary mixtures of these proteins at total concentrations of up to about 40 g/L were measured at different values of the pH and ionic strength. At the pH values of measurement, ovalbumin and ovomucoid have a net negative charge and ribonuclease A has a net positive charge. The observed dependence of scattering intensity upon solution composition may be accounted for by an extension of previously formulated equivalent hard particle models that allows for the presence of both repulsive interactions between like species and attractive interactions between unlike species in mixtures of positively and negatively charged proteins.

Quantifying the co-solvent effects on trypsin from the digestive system of carp Catla catla by biophysical techniques and molecular dynamics simulations

Urea molecules locate within 0.5 nm of the surface of trypsin.