Enzymological characteristic of monoamine oxidase from the visual ganglia of the Pacific squid Todarodes pacificus

Abstract

The study of catalytic properties of mitochondrial monoamine oxidase (MAO; monoamine:О2 oxi� doreductase, deaminating; EC 1.4.3.4), which main� tains physiological level of mediators in the presynap� tic nerve terminal, is of general biological interest and a great importance for enzymology, in particular, for characterizing redox enzymes. The biological role of MAO is associated with the regulation of the level of mediators in nerve structures and, therefore, with dif� ferent functions of the nervous system, which is con� firmed, in particular, by experimental and clinical data on the use of MAO inhibitors [1]. The study of the sub� strate specificity and multiplicity of MAO forms in the central nervous system of different animals will proba� bly provide an opportunity to differentially determine the functional role of MAO in neural processes. The majority of available papers in this field are devoted to studying MAO of terrestrial vertebrates, whereas MAO of aquatic animals has been studied quite insuffi� ciently. It was established that neural tissues of marine invertebrates contain a relatively high MAO activity as compared to other organs [2, 3]. Monoamine oxidase activity was detected in the visual ganglia, which fulfill the function of the central nervous system, of some cephalopods, such as octopuses Octopus vulgaris [4], Eledone moschata [5], and Eledone cicchosa [6] and squids Loligo forbesi [7], Loligo pealei [8], and Berry� teuthis magister [9]. Although over 350 squid species are known in the World Ocean [10], the monoamine oxidase activity of visual ganglia has been studied so far only in a few of them [7–9], which is possible caused by difficulties in obtaining biological material. Almost all papers devoted to the MAO of visual ganglia of squids contain only qualitative results. The list of kinetically studied enzymes with enzymological parameters of substrate–inhibitor specificity is quite scanty [8]. The substrate and inhibitor analyses of monoamine oxidase activity of visual ganglia of the Pacific squid Todarodes pacificus were undoubtedly of interest. The kinetic parameters of enzymatic deamination of tyramine, serotonin, benzylamine, histamine, tryptamine, and β�phenylethylamine as well as bimo� lecular rate constants for the interaction of inhibitors deprenyl and chlorgilin with the enzyme were calcu� lated. It should be noted that this was the first work to study the catalytic properties of MAO from the visual ganglia of this commercially important squid species.