THE RELATIONSHIP BETWEEN pH AND THE ACTIVITY OF CHOLINESTERASE FROM FLIES

Abstract

Variation in activity of fly head cholinesterase (ChE) was measured titrimetrically at 25 degrees C with acetyl choline bromide 0.015 [image] as substrate, as a function of the pH of the assay medium over the range from pH 4.0 to 10.0. Ground tissue obtained from Musca domestica L. was suspended at a concentration of one head per ml. in 3 media: (1) NaCl-KH2PO4 buffer; (2) 30% glycerol; (3) de-ionized water. Enzymic activity was greater in buffer than in the other media. The pH optimum was between pH 8.0 and 9.0. Some permanent inactivation of the enzyme was observed in half-hour exposures at high and low pH values. Inactivation of ChE resulting from exposure to low or high pH was not reversed during subsequent incubation of the sample at pH 8.0 for as long as 18 hours. The degree of permanent inactivation is slight within pH limits where the pH-activity curve is measured.