Rapid reagent-less detection of competitive inhibitors of butyrylcholinesterase

Monosulfonate tetraphenyl porphyrin (TPPS1) competitively inhibits horse serum butyrylcholinesterase (BChE). The interaction of TPPS1 with the active site of BChE results in a decrease in TPPS1 absorbance at 398 nm and the appearance of a new absorbance peak centered at 429 nm. The interaction of TPPS1 with immobilized BChE yields a characteristic absorbance peak at 421 nm. Exposure of the immobilized TPPS1–BChE surface to competitive inhibitors but not non-competitive inhibitors of BChE results in a loss in absorbance of the 421 nm peak due to the displacement of the porphyrin from the active site. The change in absorbance is proportional to the inhibitor concentration with detection limits of 50 ppt eserine, 72 ppt amitriptyline, 91 ppt drofenine, and 40 ppb Triton X-100.