A bi-fluorescence-labeled substrate for ceramide glycanase based on fluorescence energy transfer

Interpenetrating Polymer Network Capturing FRET-Sensitive Polymers Available for an Enzyme Assay

Fluorogenic glycomonomers have been used for biological evaluations, and water-soluble and Förster resonance energy transfer (FRET)-sensitive glycopolymers have also been reported. A FRET-sensitive polymer was conveniently prepared from a fluorogenic donor monomer and a fluorogenic acceptor monomer by means of simple radical polymerization in high yield. Continuous fluorospectroscopic monitoring of the polymer in the presence of an enzyme was performed, and the results showed the possible application of the FRET-sensitive glycopolymer for practical use. In addition to the use of aqueous solution phase, the water-soluble and FRET-sensitive glycopolymer was completely captured into an interpenetrating polymer network (IPN) by means of radical polymerization with a combination of acrylamide and bis-acrylamide as used for the cross-linking reagent system. The IPN including the FRET-sensitive glycopolymer was allowed to react with amylases in an aqueous buffer solution at 37 °C, and the enzymatic reaction was continuously and conveniently monitored by means of fluorometric spectroscopy.

Synthetic studies of bi-fluorescence-labeled maltooligosaccharides as substrates for α-amylase on the basis of fluorescence resonance energy transfer (FRET)

A series of bi-fluorescence-labeled maltooligosaccharides that lead to fluorescence resonance energy transfer (FRET) was systematically synthesized. Effective FRETs were observed with all of the synthesized probes. Digestion of probes having tetra-, quintet-, hexa- or hepta-saccharidic chain lengths with human saliva α-amylase resulted in disappearance of FRET when an excitation wavelength of at 290nm was used followed by detection at ca. 520nm due to emission from the dansyl moiety. However, continuous FRET was observed when probes having di- or trisaccharidic chain lengths were used as substrates. In addition to the substrate characteristics based on saccharidic chain length, the reaction rates of digestion for the substrates by amylase were different and also depended on their saccharidic chain length.

Activatable Optical Probes for the Detection of Enzymes

The early detection of many human diseases is crucial if they are to be treated successfully. Therefore, the development of imaging techniques that can facilitate early detection of disease is of high importance. Changes in the levels of enzyme expression are known to occur in many diseases, making their accurate detection at low concentrations an area of considerable active research. Activatable fluorescent probes show immense promise in this area. If properly designed they should exhibit no signal until they interact with their target enzyme, reducing the level of background fluorescence and potentially endowing them with greater sensitivity. The mechanisms of fluorescence changes in activatable probes vary. This review aims to survey the field of activatable probes, focusing on their mechanisms of action as well as illustrating some of the in vitro and in vivo settings in which they have been employed.

Carbosilane Dendrimers Bearing Globotriaoses: Syntheses of Globotrioasyl Derivative and Introduction into Carbosilane Dendrimers†

As an application of a one-pot reaction involving Birch reduction and subsequent S(N)2 reaction in liquid ammonia, synthetic assembly of trisaccharidic moieties of globotriaosyl ceramide onto carbosilane dendrimers was accomplished using tris(3-bromopropyl)phenylsilane and tris[tris(3-bromopropyl)silylpropyl]phenylsilane as the core scaffolds. The common globotriaosyl derivative having benzylsulfide functionality at the terminal of the aglycon was efficiently prepared from d-galactose and d-lactose as starting materials. The glycosyl donor derived from galactose and the glycosyl acceptor derived from lactose were condensed in the presence of silver triflate as the best promoter to provide corresponding trisaccharide with newly formed alpha-1-4 linkages in 90% yield. Fully benzylated protection of the trisaccharide was deprotected under the Birch reduction condition followed by acetylation to give an acetate in which alkene was converted into benzyl sulfide by radical addition of alpha-toluenethiol in high yields. On the other hand, carbosilane dendrimers were prepared from appropriate chlorosilanes as starting materials by a combination of hydrosylation followed by alkenylation. The terminal C=C double bonds of the carbosilanes were converted into corresponding alcohols by means of the usual hydroboration reaction, and the alcohols underwent further chemical manipulation to give carbosilane dendrimers with peripheral bromine atoms.

Design of fluorogenic substrates for continuous assay of sialyltransferase by resonance energy transfer

Glycosyltransferases are important synthetic enzymes for the construction of naturally occurring glycoconjugates as well as for the design of neoglycoconjugates. The assay methods currently available for these enzymes require tedious and time-consuming procedures for separation of products and do not permit continual assay of enzyme activities. As a set of convenient fluorogenic substrates for continuous monitoring of sialyltransferase activities, we designed and synthesized a novel CMP-Neu5Ac derivative with a naphthylmethyl group at the C-9 position and N-acetyllactosamine derivative containing a dansyl group at the terminal position of aglycon. In such substrates, the emission peak of the naphthylmethyl group (lambdaem = 340 nm) of the glycosyl donor is successfully overlapped with the excitation peak due to the dansyl group (lambdaex = 335 nm) of the glycosyl acceptor. A coupling reaction of these two substrates catalyzed by rat liver 2,6-sialyltransferase caused an increase of dansyl fluorescence (lambdaem = 525 nm) and a decrease of naphthylmethyl fluorescence on the basis of resonance energy transfer between two fluorescence probes. The substrates presented here permit continuous fluorescent monitoring of enzymatic sugar combining reactions. Actually, using this time course of enzymatic reactions, kinetic constants of rat liver 2,6-sialyltransferase against glycosyl donor substrates were estimated to be Km = 4.85 microM and Vmax. = 0.119 micromol/min, respectively. This strategy allows precise and efficient analyses of enzyme kinetics not possible with the conventional assay methods for the glycosyltransferases that usually require separation of products from the reaction mixture.