A comparative study has been made of the anticholinesterase activities of the methiodides and hydrochlorides of anabasine, lupinine, anabasamine, and methyl aphyllinate, which have proved to be reversible inhibitors of two types of cholinesterases.Among the derivatives of various alkaloids [1-3], compounds have been found that undergo catalytic hydrolysis under the action of cholinesterases (ChEs) and may therefore be assigned to the synthetic substrates of these enzymes. However, other derivatives of this series of substances cause inhibition of ChE activity, i.e., are ChE inhibitors.By various methods [4-10], 10 alkaloids have been isolated from the plant Anabasis aphyUa growing in the Central Asian region. Structural differences and the presence of reactive groupings, and also conformational features of these alkaloids, may play an important role in the manifestation of a biological effect.We have studied the dependence of the cholinergic activity of anabasine, lupinine, anabasamine, and methyl anaphyllinate on their structural features.Starting from the structures of these alkaloids, it is not difficult to assume that as the result of their interaction with a ChE an enzyme-sorption complex is formed with the anionic point of the ChE located on the active surface of such a hydrolase. The screening of this section of the alkaloid molecule interferes with the access of the substrate to the active center, a consequence of which is a decrease in the catalytic hydrolysis of acetylcholine under the action of the ChE. All the alkaloids under investigation are nitrogen-containing heterocycles and their structure is close to the ammonium "head" of the ChE substrate acetylcholine. At physiological pH values, these groupings are capable of undergoing protonation and, consequently, of ion-ion interaction with the anionic point of the ChE. The inhibition of the activities of acetylcholinesterase (ACHE) and butyrylcholinesterase (BuChE) by the alkaloids did not depend on the time of incubation, which shows the reversible nature of the inhibition of the activity of the hydrolases under study. Table 1 gives the constants of reversible inhibition of AChE and BuChE by the alkaloids of Anabasis aphylla. It can be seen that, with the exception of the alkaloid anabasamine, these substances are inhibitors of moderate strength. Among the alkaloids studied, lupinine hydrochloride is a strong inhibitor of BuChE, and anabasine methiodide of ACHE. While the former inhibits the activity of BuChE by the mixed type of inhibition, the latter interacts with AChE without competing for the substrate-binding section.Anabasine hydrochloride, methiodide, and sulfate inhibit AChE activity equally strongly. In the case of BuChE, anabasine hydrochloride exhibits a greater effectiveness than its methiodide and sulfate. Lupinine -quantitatively the second alkaloid of Anabasis aphylIainhibits the activities of both types of ChE predominantly by the mixed type of action. The hydrochloride is most active in relation to BuChE, while on interaction with AC...