Acetylcholinesterase (AChE), a serine hydrolase, is potentially susceptible to inactivation by phenylmethylsulfonyl fluoride (PMSF) and benzenesulfonyl fluoride (BSF). Although BSF inhibits both mouse and Torpedo californica AChE, PMSF does not react measurably with the T. californica enzyme. To understand the residue changes responsible for the change in reactivity, we studied the inactivation of wild-type T. californica and mouse AChE and mutants of both by BSF and PMSF both in the presence and absence of substrate. The enzymes investigated were wild-type mouse AChE, wild-type T. californica AChE, wild-type mouse butyrylcholinesterase, mouse Y330F, Y330A, F288L, and F290I, and the double mutant T. californica F288L/F290V (all mutants given T. californica numbering). Inactivation rate constants for T. californica AChE confirmed previous reports that this enzyme is not inactivated by PMSF. Wild-type mouse AChE and mouse mutants Y330F and Y330A all had similar inactivation rate constants with PMSF, implying that the difference between mouse and T. californica AChE at position 330 is not responsible for their differing PMSF sensitivities. In addition, butyrylcholinesterase and mouse AChE mutants F288L and F290I had increased rate constants ( approximately 14 fold) over those of wild-type mouse AChE, indicating that these residues may be responsible for the increased sensitivity to inactivation by PMSF of butyrylcholinesterase. The double mutant T. californica AChE F288L/F290V had a rate constant nearly identical with the rate constant for the F288L and F290I mouse mutant AChEs, representing an increase of approximately 4000-fold over the T. californica wild-type enzyme. It remains unclear why these two positions have more importance for T. californica AChE than for mouse AChE.
Title: [Partial characteristics of the basic phenylmethylsulfonylfluoride-inhibited carboxypeptidase from cat brain] Vernigora AN, Nikishin NN, Gengin MT Ref: Biokhimiia, 60:1860, 1995 : PubMed
Cat brain carboxypeptidase releasing C-terminal arginine from the synthetic substrate, dansyl-Phe-Leu-Arg, was partially characterized. The enzyme has a molecular weight of 100-120 kDa, displays the maximal activity at pH 6.0-6.5 and is strongly inhibited by phenylmethanesulfonylfluoride and 4-chloromercuribenzoate, less strongly (by 40%) by iodoacetamide and is not inhibited by N-ethylmaleimide, 2-mercaptoethanol, EDTA, Co2+ and guanidinoethylmercaptosuccinic acid. The Km values for the hydrolysis of dansyl-Phe-Leu-Arg and dansyl-Phe-Ala-Arg by soluble carboxypeptidase are 48 and 96 microM, respectively. By all properties, this carboxypeptidase differs from other known carboxypeptidases. Possible participation of the enzyme in neuropeptide metabolism is discussed.
Title: Sciatic nerve neuropathy target esterase. Methods of assay, proximo-distal distribution and regeneration Barril JB, Vilanova E, Pellin MC Ref: Toxicology, 49:107, 1988 : PubMed
Some organophosphorus compounds (OP) induce a delayed polyneuropathy (OPIDP) which is initiated by the phosphorylation of the so-called neuropathy target esterase (NTE). In this work some aspects of hen sciatic nerve NTE are studied. The assay method is reported and modifications are discussed and a combined method proposed. Proximo-distal distribution showed a significant difference from proximal (100 +/- 10%) to distal (69 +/- 9%) fragments, in accordance with reported data. The time course of in vivo regeneration after a single TOCP dose (200 mg/kg, post oral) showed some differences when compared with hen brain NTE. Sciatic nerve NTE showed a delay of 2-3 days before regeneration but then regenerated faster (74% activity at day 7) than brain NTE (50% activity at day 7). A slower rate of regeneration of distal than proximal segments has been suggested to explain higher sensitivity of distal segments [3], however in this work no significant differences were observed in the rate of regeneration when comparing proximal and distal fragments.
