Comparative Study of Catalytic Properties of Monoamine Oxidases of the Liver of the Squid Todarodes pacificus and of the Liver of the Wistar Rat

Abstract

A comparative study of substrate specificity of monoamine oxidase (MAO) in mitochondria of liver of the Pacific squid Todarodes pacificus and of Wistar rats is carried out. It is revealed that the squid liver MAO, unlike the rat liver MAO, is capable of deaminating not only tyramine, serotonin, and benzylamine, but also histamine. The squid liver MAO activity in relation to all studied substrates is approximately 10 times lower, while the sorption ability, several tens times lower, than the rat liver MAO. Semicarbazide, a classic inhibitor of diamine oxidase, at a concentration 1 × 10−2 M did not inhibit the catalytic activity of both studied enzymes. The specificity of action of an irreversible inhibitor, proflavine, is established, which was seen at deamination of various substrates by the squid liver MAO to the greater degree, than by the rat liver MAO. The values of the bimolecular rate constant of the irreversible inhibition (kII) by proflavine were 2.5–20-fold higher (depending on substrate) in the case of the squid liver MAO, than of the rat liver MAO. A suggestion is put forward about the probable presence of several centers of substrate binding in the enzyme of the studied marine invertebrate, like in the mammalian enzyme.