THE EFFECT OF VARIOUS SUSPENSION MEDIA ON THE ACTIVITY OF CHOLINESTERASE FROM FLIES

Abstract

1. The cholinesterase (ChE) activity of fly-head suspensions was measured titrimetrically at 25.0 degrees C. and pH 8.0 with acetylcholine bromide 0.015 M as substrate, as a function of the concentration of various single salts, glycerol, or sucrose. The species tested was Musca domestica L. 2. The salts, NaCl, KCl, MgCl₂, CaCl₂, NaNO₃, (NH₄)₂,SO₄, at concentrations up to 0.5 to 1.0 N, had a non-specific activating effect. At still higher concentrations, activity was depressed progressively below the maximum, which was two to three times the value observed with water suspensions. 3. None of the ions tested was found essential to the activity of fly-head ChE. MgCl₂, was slightly but significantly more potent as an activator than NaCl. 4. Both glycerol and sucrose were depressant at all concentrations tested. The relationship was linear with concentration. For glycerol, the slope was about - 14 per cent per mole and for sucrose, about - 31 per cent per mole. 5. The depression of activity in the presence of higher concentrations of salts, glycerol or sucrose was not relieved by a four-fold increase in substrate concentration. 6. It is inferred that the changes in activity observed reflect alterations of an unknown nature in the properties of the enzyme, rather than direct interference with access of substrate to the active sites.