Comparative enzymological study of catalytic properties of liver monoamine oxidases in frogs

Abstract

Comparative enzymological study of catalytical properties of monoamine oxidase (MAO) of liver of the lake frog Rana ridibunda and brown frog Rana temporaria has revealed certain features of similarity and differences between these enzymes. The MAOs from both studied biological sources show catalytic properties resembling those of the classical MAO of terrestrial vertebrates: they deaminate tyramine, tryptamine, serotonin, benzylamine and do not deaminate histamine, have sensitivity to chlorgiline, the specific inhibitor of the MAO A form, and deprenyl, the specific inhibitor of the MAO B form, and are not inhibited with 10(-2) M semicarbazide. Based on data of substrate-inhibitor analysis, a suggestion is put forward about the existence of two molecular forms of the enzyme in liver of the studied frog species. Interspecies quantitative differences have been revealed between liver MAO of Rana ridibunda and Rana temporaria in values of kinetic parameters of reactions of deamination of several substrates and in sensitivity to the inhibitors, deprenyl and clorgyline. In the species Rana temporaria the MAO activity in reaction of deamination of serotonin and benzylamine were practically identical, whereas in the species Rana ridibunda these parameters for serotonin were almost one order of magnitude higher than for benzylamine. For the species Rana ridibunda, selectivity of action of deprenyl was expressed many times weaker while selectivity of the chlorgiline--one order of magnitude stronger than for the species Rana temporaria. The catalytic activity for all studies substrates of liver MAO of both studied amphibian species were several times lower as compared with the enzyme of rat liver.