[New weak toxins from the cobra venom].

A protein with M 7485 Da containing five disulfide bonds was isolated from the venom of cobra Naja oxiana using various types of liquid chromatography. The complete amino acid sequence of the protein was determined by protein chemistry methods, which permitted us to assign it to the group of weak toxins. This is the first weak toxin isolated from the venom of N. oxiana. In a similar way, two new toxins with M 7628 and 7559 Da, which fall into the range of weak toxin masses, were isolated from the venom of the cobra N. kaouthia. The characterization of these proteins using Edman degradation and MALDI mass spectrometry has shown that one of these proteins is a novel weak toxin and the other is the known weak toxin WTX with an oxidized methionine residue in position 9. Such a modification was detected in weak toxins for the first time. A study of the biological activity of the toxin from N. oxiana showed that, like other weak toxins, it can be bound by muscle nicotinic cholinoreceptors and alpha7 nicotinic cholinoreceptors.

[Study of the molecular structure and mechanisms of pond snail neuron cholinoreceptor function by means of in vivo chemical modification]. / Issledovanie molekuliarnoi struktury i mekhanizmov funktsionirovaniia kholinoretseptorov neironov prudovika s pomoshch'iu prizhiznennoi khimicheskoi modifikatsii.

The molecular structure of acetylcholine receptors (AChR) of Lymnaea stagnalis neurons has been studied using specific agents to definite chemical groups. The disulphide bond important for AChR function was discovered, the reduction of which by dithiotreitol (DTT) inactivates AChR. The drugs exciting AChR protect the disulphide bond against modification with DTT likely due to the conformational changes of an active site and its environment. Desensitized AChR can also be modified by DDT (if it is not occupied by agonist). It is suggested that the system transmitting the conformational change from the AChR active site to its ionophore is responsible for desensitization.

[Effect of pH on properties of the cholinoreceptive membrane of snail neurons]. / Vliianie pH na svoistva kholinoretseptivnoi membrany neironov prudovika

The influence of pH on acetylcholine (ACh)-induced responses in completely isolated neurons of Lymnaea stagnalis was studied under voltage clapm conditions. The pH drop lead to a decrease in sensitivity of cholinoreceptive membrane; at pH 5.8-6.0 ACh-responses were eliminated completely. When raising the external pH (up to 10.6) there were no changes in the ACh effect. A group responsible for sensitivity changes of the cholinoreceptive membrane appears to have pK about 6.7. It is shown that the pH drop does not influence the ionic channel functional groups. The results can be explained in the assumption that some functionally important groups in the cholinoreceptor active site are protonated at low pH.