Colorimetric Assay for S-Adenosylhomocysteine Hydrolase Activity and Inhibition Using Fluorosurfactant-Capped Gold Nanoparticles

This study reports a simple colorimetric method for the sensitive detection of S-adenosylhomocysteine hydrolase (SAHH) activity and inhibition using fluorosurfactant-capped gold nanoparticles (FSN-AuNPs). FSN stabilizes the AuNPs against conditions of high ionic strength, and FSN-AuNPs are merely aggregated in the presence of homocysteine (HCys) and cysteine. Because of this feature, FSN-AuNPs were found to be dispersed in the presence of S-adenosylhomocysteine (SAH) that lacks a free thiol group. After SAHH catalyzed the hydrolysis of SAH, the produced HCys molecules were bound to the surface of AuNPs through the formation of Au-S bonds. As a result, the nanoparticle (NP) aggregation occurred through electrostatic attraction between each HCys-attached AuNP. This approach had a minimum detectable concentration of 100 units/L (similar to 6 nM). Additionally, because adenosine analogs are capable of inhibiting SAHH activity, the addition of adenosine analogs to a solution containing SAH and SAHH resulted in the suppression of hydrolyzed SAH-induced NP aggregation. Adenosine analogs exhibited the following trend in the half-maximal inhibitory concentrations: adenosine > adenosine monophosphate > adenosine diphosphate similar to adenosine triphosphate. We have demonstrated that the combination of SAHH inhibition and FSN-AuNPs can be utilized for the selective detection of adenosine.