Sensitive and rapid electrochemical bioassay of glycosidase activity

Recent advances in the development of synthetic chemical probes for glycosidase enzymes

The emergence of synthetic glycoconjugates as chemical probes for the detection of glycosidase enzymes has resulted in the development of a range of useful chemical tools with applications in glycobiology, biotechnology, medical and industrial research. Critical to the function of these probes is the preparation of substrates containing a glycosidic linkage that when activated by a specific enzyme or group of enzymes, irreversibly releases a reporter molecule that can be detected. Starting from the earliest examples of colourimetric probes, increasingly sensitive and sophisticated substrates have been reported. In this review we present an overview of the recent advances in this field, covering an array of strategies including chromogenic and fluorogenic substrates, lanthanide complexes, gels and nanoparticles. The applications of these substrates for the detection of various glycosidases and the scope and limitations for each approach are discussed.

Human intestinal hydrolysis of phenol glycosides - a study with quercetin and p-nitrophenol glycosides using ileostomy fluid

In order to study the influence of sugar moiety, aglycon structure and microflora concentration on the human ileal hydrolysis of phenol glycosides, various quercetin and p-nitrophenol glycosides were incubated under anaerobic conditions (37 degrees C for 0, 0.5, 1, 2, 4, 6, 8, 10 and 24 h) with ileostomy fluids from three different donors. The glycosides, i.e. beta-D-glucopyranosides, beta-D-galactopyranosides, alpha-L-arabinofuranosides, beta-D-xylopyranosides and alpha-L-rhamnopyranosides as well as the liberated aglycones were identified by HPLC-DAD and HPLC-ESI-MS/MS. Among the quercetin glycosides under study, the 3-O-beta-D-glucopyranoside showed with 0.22 micromol/h the highest hydrolysis rate, followed by the 3-O-beta-D-galactopyranoside, the 3-O-beta-D-xylopyranoside and the 3-O-alpha-L-arabinofuranoside (0.04 and each 0.03 micromol/h, respectively). Quercetin 3-O-alpha-L-rhamnopyranoside was found to be stable for the entire incubation period. Using quercetin 3-O-beta-D-glucopyranoside as a representative example, linear hydrolysis rate was observed from 75 to 2500 microL ileostomy fluid corresponding to its microflora content (log 0.68 up to 21.9 colony forming units). Studies performed in the presence of antibiotics did not reveal any hydrolysis. The p-nitrophenol glycosides were hydrolyzed faster than the corresponding quercetin glycosides. The hydrolysis rate decreased from the beta-D-glucopyranoside (0.41 micromol/h), to the beta-D-galactopyranoside (0.21 micromol/h), the beta-D-xylopyranoside (0.12 micromol/h), the alpha-L-arabinofuranoside (0.09 micromol/h) to the alpha-L-rhamnopyranoside (0.06 micromol/h). These results demonstrate that the human ileal hydrolysis of phenol glycosides depends on the sugar and the aglycon structure as well as the microflora.