[Comparative study of substrate and inhibitory specificity of monoamine oxidase in the optic ganglia of squids].

Comparative study of substrate specificity of monoamine oxidase (MAO) of optic ganglia of the Pacific squid Todarodes pacificus and the Commander squid Berryteuthis magister has been carried out. The enzyme of the Pacific squid, unlike that of the Commander squid, has been established to be able to deaminate not only tyramine, tryptamine, serotonin, benzylamine, and beta-phenylethylamine, but also histamine--substrate of diamine oxidase (DAO). In relation to all studied substrates, the MAO activity of optic ganglia of T. pacificus is several times higher as compared with B. magister. In the case of deamination of serotonin this difference was the greatest and amounted to 5 times. Semicarbazide, the classic DAO inhibitor, at a concentration of 10 mM did not inhibit catalytic activity of both studied enzymes. The substrate-inhibitory analysis with use of deprenyl and chlorogiline, specific inhibitors of different MAO forms, indicates homogeneity of the enzyme of the Pacific squid and heterogeneity of the Commander squid enzyme whose composition seems probably to contain at least two MAO forms. There are obtained quantitative differences in substrate specificity and reaction capability with respect to the inhibitors chlorgiline and deprenyl for MAO of optic ganglia of the studied squid species. These differences probably can be explained by significant differences in the evolutionary level of these biological species.