Enzyme-catalyzed peptide synthesis in ice

A new method for increasing product yield in kinetically controlled enzymatic peptide synthesis catalyzed by serine and cysteine proteases is proposed - freezing the reaction mixture. The use of the method in preparative synthesis has been demonstrated.     

The Influence of Inorganic Salts on the Inhibition of Acetylcholinesterase by O,O-Diethylthiophosphates

Abstract

The influence of various inorganic salts (NaCl, KCl, CsCl, KNO₃, Na₂SO₄, K₂SO₄, MgCl₂, CaCl₂) on the kinetics of the reactions of acetylcholinesterase with neutral and cationic 0,O-diethylthiophosphates, (C₂H₅0)₂ P(0)SX, where × = (CH₂)_n and (CH₂)_n S⁺ (CH₃) C₂H₅ (n=1–6), has been studied at 25° C and pH 7.5. The salt effect in the second-order rate constant can be quantitatively described by the equation log(k₂/K_s) = log(k₂ /K_S)°-ψlog[M] + bc where bc is the term for the kinetic salting effect, ψlog[M] is the electrostatic term, c and [MI are the molar concentrations of salt and salt cation. The salting effect is observed in the binding step (K_s) as well as in the enzyme phosphorylation step (k₂). Parallel increase of b with increasing n has been observed for the series of both ionic and neutral inhibitors. Electrostatic effect is observed only in the binding step for cationic inhibitors and does not depend on the distance between the onium atom and the reaction center in the inhibitor molecule. The observation of uniform Y is in accordance with the Manning's polyelectrolyte theory, suggesting that acetylcholinesterase can be considered as negatively charged polyelectrolyte. According to the theory the release of condensed counterions from the polyelectrolyte provides electrostatic contribution to the binding of cationic ligands, and the presence of localized anionic site on the acetylcholinesterase molecule is not required to account for the observed electrostatic effect. The obtained mean value of ψ = 0.49 ± 0.08 can be used as a quantitative parameter to characterize the effective charge density of acetylcholinesterase.     

Synthesis of some O,O-diethylphosphoric acid thioesters

Conclusions We synthesized a number of O,O-diethyl S-(-ethylmercaptoalkyl) thiophosphates, and their methyl methosulfates and ethyl ethosulfates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 426–428, February, 1976.     

QSAR in Reactions of Organophosphorus Inhibitors with Acetylcholinesterase

Abstract

Structure-activity relationships in inhibition of acetylcholinesterase by organophosphorus compounds (YO)(Z)P(O)SX have been analyzed using the equation log k_i = C + ρσ + ?π with Taft σ* for substituent elehtronegativity and Hansch Π for hydrophobicity. The obtained relationships have been used for optimizing the structures of organophosphorus inhibitors for their maximum anticholinesterase activity.