2009 Volume 25 Issue 2 Pages 267-273
A colorimetric change of gold nano-composites conjugated with a thermo-responsive copolymer has been applied to a colorimetric assay to quantify the activity of aminopeptidase N (APN). Heating a solution of assembled gold nano-composites provokes the gold nano-composites to disassemble, leading to a colorimetric change in the solution from blue-purple to red. The disassembly is inhibited by cysteine, but not by cysteinylglycine, thus allowing us to monitor the progress of an enzymatic decomposition of cysteinylglycine into cysteine and glycine with APN. The activity of APN is estimated through a colorimetric change in a solution of gold nano-composites from blue-purple to red, after being heated (98°C for 30 min), followed by being cooled. A good relationship between the a* value in L*a*b* color coordinates, which quantified the color of the solution, and the activity of APN was obtained in 3 h of the incubation time, indicating the potential of a colorimetric assay of APN activity.