Enzyme activity of α-chymotrypsin: Deactivation by gold nano-cluster and reactivation by glutathione

Effect of gold nanoclusters (Au-NCs) on the circular dichroism (CD) spectra and enzymatic activity of α-chymotrypsin (ChT) (towards hydrolysis of a substrate, N -succinyl- l -phenylalanine p -nitroanilide) are studied. The CD spectra indicate that on binding to Au-NC, ChT is completely unfolded, resulting in nearly zero ellipticity. α-chymotrypsin (ChT) coated gold nano-clusters exhibit almost no enzymatic activity. Addition of glutathione (GSH) or oxidized glutathione (GSSG) restore the enzyme activity of α-chymotrypsin by 30–45%. ChT coated Au-NC exhibits two emission maxima-one at 480 nm (corresponding to Au 10 ) and one at 640 nm (Au 25 ). On addition of glutathione (GSH) or oxidized glutathione (GSSG) the emission peak at 640 nm vanishes and only one peak at 480 nm (Au 10 ) remains. MALDI mass spectrometry studies suggest addition of glutathione (GSH) to α-chymotrypsin capped Au-NCs results in the formation of glutathione-capped Au-NCs and α-chymotrypsin is released from Au-NCs. CD spectroscopy indicates that the conformation of the released α-chymotrypsin is different from that of the native α-chymotrypsin.