Quantitative analysis of glycerol levels in human urine by liquid chromatography–tandem mass spectrometry

Chemical labeling strategies for small molecule natural product detection and isolation

Covering: Up to 2020.It is widely accepted that small molecule natural products (NPs) evolved to carry out a particular ecological function and that these finely-tuned molecules can sometimes be appropriated for the treatment of disease in humans. Unfortunately, for the natural products chemist, NPs did not evolve to possess favorable physicochemical properties needed for HPLC-MS analysis. The process known as derivatization, whereby an NP in a complex mixture is decorated with a nonnatural moiety using a derivatizing agent (DA), arose from this sad state of affairs. Here, NPs are freed from the limitations of natural functionality and endowed, usually with some degree of chemoselectivity, with additional structural features that make HPLC-MS analysis more informative. DAs that selectively label amines, carboxylic acids, alcohols, phenols, thiols, ketones, and aldehydes, terminal alkynes, electrophiles, conjugated alkenes, and isocyanides have been developed and will be discussed here in detail. Although usually employed for targeted metabolomics, chemical labeling strategies have been effectively applied to uncharacterized NP extracts and may play an increasing role in the detection and isolation of certain classes of NPs in the future.

Fast LC-MS quantitation of glucose and glycerol via enzymatic derivatization

Glucose and glycerol are important circulating metabolites. Due to poor ionization and/or ion suppression, the liquid chromatography-mass spectrometry (LC-MS) detection of glucose and glycerol presents challenges. Here, we propose an efficient LC-MS method of quantitative glucose and glycerol detection via enzymatic derivatization to glucose-6-phosphate and sn-glycerol-3-phosphate, respectively. This derivatization protocol can be used to measure the concentrations of glucose production in a plethora of sample types for metabolic analysis and is compatible with the general metabolomics workflow. This novel approach allows us to quantitatively study glucose and glycerol metabolism using stable isotope tracers in vivo.

Simultaneous determination of alcohols including diols and triols by HPLC with ultraviolet detection based on the formation of a copper(II) complex

We developed a reversed-phase high-performance liquid chromatography method with ultraviolet detection using on-line complexation with Cu(II) ion for analysis of five alcohols including diols and triol (methanol, ethanol, 1,2-propanediol, 1,3-propanediol, and glycerol). The Cu(II) ion concentration in the mobile phase had a great influence on the peak areas of these alcohols, but not on their retention times. Column temperature (25-40°C) and pH of the mobile phase did not affect the separation of analytes. The optimum separation conditions were determined as 5 mM CuSO₄ , 3 mM H₂ SO₄ , and 3 mM NaOH at 30°C. The ratio of the peak areas for three alcohols (methanol, 1,2-propanediol, and glycerol) was in good agreement with that calculated from the obtained stability constants, molar absorption coefficients for the 1:1 Cu(II) complexes with the three alcohols, and the injected molar quantities. This fact strongly suggests that the observed high-performance liquid chromatography signals resulted from formation of the 1:1 Cu(II)-alcohol complexes. Using the proposed method, these five alcohols in spirit, liquid for electronic cigarette, mouthwash, and nail enamel remover samples were successfully analyzed with only a simple pretreatment.

Glycerol kinase of African trypanosomes possesses an intrinsic phosphatase activity

BACKGROUND

In general, glycerol kinases (GKs) are transferases that catalyze phospho group transfer from ATP to glycerol, and the mechanism was suggested to be random bi-bi. The reverse reaction i.e. phospho transfer from glycerol 3-phosphate (G3P) to ADP is only physiologically feasible by the African trypanosome GK. In contrast to other GKs the mechanism of Trypanosoma brucei gambiense glycerol kinase (TbgGK) was shown to be in an ordered fashion, and proceeding via autophosphorylation. From the unique reaction mechanism of TbgGK, we envisaged its potential to possess phosphatase activity in addition to being a kinase.

METHODS

Our hypothesis was tested by spectrophotometric and LC-MS/MS analyses using paranitrophenyl phosphate (pNPP) and TbgGK's natural substrate, G3P respectively. Furthermore, protein X-ray crystallography and site-directed mutagenesis were performed to examine pNPP binding, catalytic residues, and the possible reaction mechanism.

RESULTS

In addition to its widely known and expected phosphotransferase (class II) activity, TbgGK can efficiently facilitate the hydrolytic cleavage of phosphoric anhydride bonds (a class III property). This phosphatase activity followed the classical Michaelis-Menten pattern and was competitively inhibited by ADP and G3P, suggesting a common catalytic site for both activities (phosphatase and kinase). The structure of the TGK-pNPP complex, and structure-guided mutagenesis implicated T276 to be important for the catalysis. Remarkably, we captured a crystallographic molecular snapshot of the phosphorylated T276 reaction intermediate.

CONCLUSION

We conclude that TbgGK has both kinase and phosphatase activities.

GENERAL SIGNIFICANCE

This is the first report on a bifunctional kinase/phosphatase enzyme among members of the sugar kinase family.

Applications and challenges in using LC–MS/MS assays for quantitative doping analysis

LC–MS/MS is useful for qualitative and quantitative analysis of ‘doped’ biological samples from athletes. LC–MS/MS-based assays at low-mass resolution allow fast and sensitive screening and quantification of targeted analytes that are based on preselected diagnostic precursor–product ion pairs. Whereas LC coupled with high-resolution/high-accuracy MS can be used for identification and quantification, both have advantages and challenges for routine analysis. Here, we review the literature regarding various quantification methods for measuring prohibited substances in athletes as they pertain to World Anti-Doping Agency regulations.