The partial purification and properties of a cholinesterase from Blatella germanica L.

Enzymes hydrolysing acetylcholine have attracted much attention because acetylcholine is concemed with the functioning of the nervous system. The extensive literature on cholinesterases has been reviewed at intervals (Zeller, 1948; Koelle & Gilman, 1949; Augustinsson, 1950; Nachmansohn & Wilson, 1951; Whittaker, 1951; Davies, 1954; Bergmann, 1958; Davies & Green, 1958). Although there is ample evidence that enzymes responsible for the hydrolysis of acetylcholine vary from species to species they can be divided roughly into types according to certain general properties (Augustinsson, 1957); one of these types is closely, but not exclusively, associated with nervous tissues. It is generally supposed that insect cholinesterases do not differ significantly from cholinesterases from other sources and that they are associated with the nervous system. However, most of the limited studies on insect cholinesterases have been made with crude breis of whole insects or parts of insects which may contain other esterases or substances that modify the activity of the cholinesterase. It is desirable to free the cholinesterase from contaminants and compare its properties with those of esterases from other sources. Any unusual properties of the enzyme might give an insight into the functioning of insect nervous tissues. In addition the properties of insect cholinesterase are ofespecial importance in relation to the mode of action of organophosphorus insecticides, which are generally considered to act by inhibiting cholinesterase of the nervous system. Doubts have been expressed that this is always the mode of action in insects, although it is well established that both cholinesterase and acetylcholine are associated with insect nervous tissues. The evidence has recently been reviewed by Winteringham & Lewis (1959). Detoxication, rate of entry of poison and other similar factors may be expected to modify the toxicity of an insecticide, but not to the exclusion of effects due to the properties of the enzyme inhibited by the poison. A knowledge of insect cholinesterases should therefore asist the understanding of the toxic action of organophosphorus compounds even if cholinesterase inhibition is not invariably the primary action of this important group of insecticides. The German cockroach (Blatella germanica L.) was chosen as the source ofan insect cholinesterase, because it is easily reared and cholinesterase activity is readily demonstrated in extracts from it. The cockroach cholinesterase differs from those examined from other sources in several interesting ways.