Interaction of monosulfonate tetraphenyl porphyrin, a competitive inhibitor, with acetylcholinesterase

Abstract

Monosulfonate tetraphenyl porphyrin (TPPS 1) forms a 1:1 complex with electric eel acetylcholinesterase (AChE) inducing a loss in TPPS 1 absorbance at 402 nm and the appearance of a new absorbance centered at 442 nm. In the presence of AChE, the fluorescence of TPPS 1 at 652 nm is slightly narrowed, with the maximal 652 nm fluorescence shifted from 407 to 412 nm excitation wavelength. The fluorescence peak of TPPS 1 at 712 nm shifts to 716 nm in the presence of AChE. TPPS 1 is a competitive inhibitor of AChE. The addition of acetylcholine iodide (AChI) or the competitive inhibitor tetracaine to the preformed AChE–TPPS 1 complex results in a loss of the 442 nm absorbance band as the porphyrin is displaced from AChE. The absorbance peak does not decrease in the presence of procaine, a non-competitive inhibitor.