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Biomedical subjects

P Hofer

Publications and source records attributed to P Hofer.

29 records · Page 2Linked to original sources
PubMed1984

Activation of acetylcholinesterase by monovalent (Na+,K+) and divalent (Ca2+,Mg2+) cations.

The activation of acetylcholinesterase [EC 3.1.1.7 (AChE)] by monovalent and divalent metal ions has been investigated by kinetic experiments under steady-state conditions (pH-stat method). It has been shown that at low ionic strength the enhancement of the activity by both monovalent and divalent metal ions can be explained as an electrostatic effect. Thereby, enhancement of the concentration of monovalent metal ions (Na+ and K+) acts by reducing the penetration depth of the electric field of carboxylate groups located at the active center whereby divalent metal ions (Ca2+ and Mg2+) act by a complex formation with these charged groups.

Acetylcholinesterase↗
PubMed1981

Acetylcholinesterase kinetics.

Three mechanisms have been suggested to describe the inhibition of acetylcholinesterase (EC. 3.1.1.7) by an excess of acetylcholine. (i) Substrate inhibition occurs through the reaction of acetylcholine with acetylated enzyme. The deacetylation of this ternary complex is supposed to be completely inhibited. (ii) A ternary complex is formed as in (i). However, the deacetylation is not completely inhibited. (iii) A two-site-mechanism is discussed. Acetylcholine binds either to the active site or to the modifier site. Binding to the latter changes the activity of the active site. Steady state treatment was applied to (i)-(iii). A least squares fit led to catalytic parameters. It is demonstrated that mechanism (ii) is the most simple one which can describe satisfactorily the experimental data. Limits for a set rate constants are derived from the catalytic parameters. A numerical integration shows that the steady state approximation may be used even when the mechanisms are rather complex.

Acetylcholine↗
PubMed1979

Structural investigation of biological material in aqueous environment by means of infrared-ATR spectroscopy.

Infrared attenuated total reflection (ATR) spectroscopy may be used to investigate biological material (e.g., membranes, proteins, erythrocytes etc.) under biological conditions provided that adhesion of the sample can be achieved in aqueous environment. Uncharged lipid multilayer model membranes can be attached by hydrophobic interaction when hydrophobic internal reflection plates (e.g., ZnSe, CdTe) are used. However, if an electric field is applied across the membrane, germanium reflection elements would be preferred because of their low electric resistance (approximately 50 omega cm). This material can also be used if cells or proteins are linked chemically to the ATR plate because of the hydrophilic surface which is similar to that of glass and, thus, enables chemical modification by silanization. It has turned out that good adhesion of uncharged and negatively charged model membranes to germanium plates is achieved when they are coated with a monomolecular layer of aminopropylsilane. There is some evidence that erythrocytes remain more stable when adsorbed to a polymerized aminosilane coating (organic silanization) rather than to the corresponding monolayer (aqueous silanization). Negatively charged germanium surfaces have been obtained by succinylation of the aminosilane coating. Furthermore it has been demonstrated that proteins can be bound to the aminosilane coating by means of carbodiimide. Immobilized acetylcholinesterase was still enzymatically active.

Acetylcholinesterase↗