Possible Interaction: Iodides and Tryptophan

“Among the amino acids tested, only cysteine affected the TPO guaiacol oxidation reaction, producing … at 25 or 50 microM. The iodide oxidation inhibitory activity of cysteine, methionine and tryptophan was … increasing iodide concentrations from 12 to 18 mM, while no such … observed when the cofactor (H2O2) concentration was increased.”

“Cs+ and I- were even less accessible than acrylamide to Trp , further proving that the Trp was located inside the lipid bilayer.”

“Moreover, the Trp of modified derivatives was less accessible for iodide than that observed with cobrotoxin.”

“Steady‐state quenching experiments indicate that Trp 21 is insensitive to quenching by iodide , but it is readily quenched by acrylamide.”

“The fraction of tryptophan residues accessible for quenching by I- decreased from 0.87 in the untreated membranes to 0.63 and 0.49 in membranes after doses of 10 and 250 Gy, respectively.”

“The emission of Trp 33 , Trp 78, Trp 171, and Trp 233 is strongly quenched by both acrylamide and iodide , whereas Trp 151 and Trp 10 display a decrease in fluorescence in the presence of acrylamide only and no quenching by iodide.”

“These tryptophans are shielded from iodide , most probably due to steric or ionic hindrances against diffusion into the binding site.”