Detection of activity and mass spectrometric identification of mouse liver carboxylesterase and aldehyde dehydrogenase separated by non-denaturing two-dimensional electrophoresis after extraction with detergents

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

A novel indene-chalcone-based fluorescence probe with lysosome-targeting for detection of endogenous carboxylesterases and bioimaging

An indene-chalcone-based fluorescence probe 1 was synthesized and characterized. Under physiological conditions (containing 5% DMSO), probe 1 showed satisfactory stability with a low background signal and recognized carboxylesterases (CEs) based on the catalytic hydrolysis of ester groups, releasing a significant green fluorescence. Probe 1 presents several features including a short response time (within 20 min), low detection limit (1.3 × 10^-4 U/mL) and large stokes shift (over 155 nm). Notably, commercial lysosomal dye co-staining experiments illustrated the lysosomal localization function of 1, with the probe also being used for cell and zebrafish imaging of endogenous CEs.

Direct analysis of retinal dehydrogenase activity on an electroblotting membrane following separation by non-denaturing two-dimensional electrophoresis

The reaction from retinal to retinoic acid catalyzed by retinal dehydrogenase on a polyvinylidene difluoride (PVDF) membrane was examined using laser desorption ionization time of flight mass spectrometry (LDI-TOF MS) when the enzyme was separated by non-denaturing two-dimensional electrophoresis (2-DE), transferred onto the membrane, and stained without impairing the enzyme activity. Furthermore, the enzyme was analyzed by de novo sequencing using electrospray ionization tandem mass spectrometry (ESI-MS/MS) after proteins from mouse liver were separated by non-denaturing 2-DE, blotted onto the membrane, and stained. The results indicated that the reported methods could be applied for the direct examination of changes in retinoid catalyzed by enzymes on such membranes.

Hydrolytic activity of lipase on anion-exchange solid phase column after separation and electrotransfer by non-denaturing electrophoresis

This study reports the initial separation of phospholipase C-alpha from porcine retina using non-denaturing two-dimensional gel electrophoresis (2-DE). Detection was by negative staining and then its hydrolytic activity was estimated using alpha-naphthyl acetate in a 2-DE gel. A spot of phospholipase C-alpha separated by 2-DE was excised. It was then electrophoretically transferred to an anion-exchange solid phase column after 40 mg, equal to dry weight of the solid resin from the cartridge (Accell Plus QMA, Waters Corporation), was packed into a disposable 1 ml syringe to make an anion-exchange solid phase column. Phosphatidylcholine was hydrolyzed in the anion-exchange solid phase column containing phospholipase C-alpha. The results indicated that a column with hydrolytic activity could be produced once lipases separated by non-denaturing 2-DE were transferred to the solid phase column.