Substrate Selectivity of Monoamine Oxidase A, Monoamine Oxidase B, Diamine Oxidase, and Semicarbazide-Sensitive Amine Oxidase in COS-1 Expression Systems

Abstract

Amine oxidases (AOs) are widely distributed among all living organisms. 1) This class of enzymes is divided into two subclasses: FAD-containing amine oxidases (FAD-AOs) and Cu-containing amine oxidases (Cu-AOs). Two types of mitochondrial monoamine oxidases, monoamine oxidases (MAO)-A and MAO-B, and cytosolic polyamine oxidase are included in FAD-AOs.2) The Cu-AOs consist of retina amine oxidase, diamine oxidase (DAO), and semicarbazide-sensitive amine oxidase (SSAO), which is known as the tissue-bound or plasma form of amine oxidase. The classification of MAO into an A and B form was primarily based on Johnston's presentation that both enzymes could be differentiated with the aid of the specific inhibition of MAO-A by clorgyline and of MAO-B by deprenyl. 3) Classification by means of specific inhibitors has been more convenient for the identification of different types of amine oxidase. However, this concept has been considered somewhat of an oversimplification and the premises on which it was based have come under increasing scrutiny. [4][5][6][7][8][9] One major problem was that serotonin and b-phenylethylamine, which are generally used to distinguish MAO-A and MAO-B, are not entirely specific for the respective MAO form. Another problem was that the substrate selectivity of MAO seems to be affected by minor cross-inhibition caused by specific inhibitors.SSAO essentially metabolizes amine compounds as well as MAO-A and MAO-B. However, the enzyme activity is not inhibited by clorgyline and deprenyl, whereas it is almost completely inhibited by semicarbazide. In contrast, semicarbazide has a weak inhibitory effect on MAO at a concentration of 0.1-1 mM. 10) Clorgyline and deprenyl have been regarded as virtually inactive against the tissue-bound SSAO, nevertheless they showed moderate reversible competitive inhibition against bovine 11) and human 12,13) plasma SSAO at a concentration of 0.1-1 mM. DAO, belonging to the Cu-AOs, is responsible for histamine metabolism. 14) Comparative substrate selectivity studies of DAO have not always been performed in detail. Aminoguanidine has been used for many years as an inhibitor of Cu-AO, but it is a relatively weak and nonselective inhibitor of SSAO. 15) Thus, the results of the substrate selectivity of these amine oxidases using specific inhibitors are very confused and complex, and might not reflect natural biochemical properties. In this study, we utilized a single amine oxidase expressed in COS-1 cells to investigate the substrate selectivity of amine oxidases in the absence of chemical inhibitors. MATERIALS AND METHODSAnimals Nine-week-old male Wistar rats purchased from Japan SLC (200-220 g, Hamamatsu, Japan) were housed at a constant temperature (23Ϯ1°C) and humidity (55Ϯ5%) with automatically controlled lighting (07:00-19:00).Plasmid Construction Standard protocols were used for all recombinant DNA technology. 16) The full-length ORF AOs plasmid was constructed as follows. Total RNA was isolated using the Wizard SV Total RNA Extraction Kit (Promega, Madison, WI,...

Recent Developments in the Regulation of Monoamine Oxidase Form and Function: Is the Current Model Restricting Our Understanding of the Breadth of Contribution of Monoamine Oxidase to Brain [dys]Function?

“…Two isoforms of MAO, i.e. MAO-A and MAO-B, have been identified according to differences in their specificities for inhibitors [20][21][22] and substrates [22][23][24][25]. MAO-A is inhibited by clorgyline at low nanomolar concentrations and this irreversible inhibitor has been used to estimate the turnover rate of MAO-A to be 2 days and recovery of MAO-A activity and protein levels after treatment with clorgyline to occur within 14 days [26].…”

Bioelimination of histamine in epithelia of the porcine proximal colon of pigs

“…5) and/or one of the MAO isoforms on the outer mitochondrial membrane [48] further oxidised 1-MH cannot finally be answered by the results of the present study. A trend to increase the 1-MH appearance after inhibition of DAO with AG ( Fig.…”

“…1-MH can also be oxidised in a second step by DAO [45][46][47] or one of the monoamine oxidases, MAO-A or MAO-B [44,48]. Histamine catabolism by the mentioned enzymes is essentially an intracellular process.…”

“…The latter is, in part, exported across the basolateral membrane via a yet unidentified mechanism. Remaining 1-MH can be oxidised sequentially by monoamine oxidase (MAO) on the outer mitochondrial membrane and cytosolic xanthine oxidoreductase (XO), giving 1-methylimidazoleacetaldehyde (MIA) and 1-methylimidazoleacetic acid (MIAA), respectively [44,48,54]. An alternative oxidation pathway for 1-MH is via DAO [45][46][47].…”

Histamine: an undercover agent in multiple rare diseases?

“…On its own, intracellular Hia can slow the G1/S progression of the cell cycle, as recently demonstrated in transfected human embryonic cells expressing active and inactive versions of HDC [5]. It can also act as a stress factor because it is degraded by amino oxidases [6]. Extracellular Hia can be taken up by organic cation transporters [7].…”