Monoamine oxidase from beef liver mitochondria: Simplified isolation procedure, properties, and determination of its cysteinyl flavin content

Salach, James I.

doi:10.1016/0003-9861(79)90078-x

Cited by 141 publications

(56 citation statements)

References 33 publications

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“…MAO was isolated from bovine liver mitochondria according to the method published by Salach (7). The specific activity of the preparation was in good agreement with that published.…”

Section: Methodssupporting

confidence: 79%

“…This enzyme preparation can be obtained with a relatively high degree of homogeneity and has been well characterized with respect to cofactor content [an 8a-S-cysteinyl flavin-adenine dinucleotide (10)] and with respect to steady-state and presteady-state kinetic properties (11). The substrate specificity and sensitivity of this enzyme preparation characterize it as the B form of the enzyme (7).…”

Section: Resultsmentioning

confidence: 99%

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N-nitrosodialkylamines do not function as substrates for liver monoamine oxidase.

Edmondson¹,

Bruice²

1985

Proc. Natl. Acad. Sci. U.S.A.

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Since reports in the literature [Rowland, I. R., Lake, B. G. & Gangolli, S. D. (1980) Mutat. Res. 72,[63][64][65][66][67][68][69][70][71][72] have implicated hepatic monoamine oxidase (EC 1.4.3.4) in the activation of N-nitrosodialkylamines to mutagens, it is of basic pharmacological and biochemical interest to determine if these compounds could serve as substrates for this enzyme. The dialkylnitrosamines N-nitrosodiethylamine, Nnitrosodimethylamine, and N-nitrosodibenzylamine were tested and found not to be substrates, competitive inhibitors, or irreversible inhibitors of liver monoamine oxidase. Thus, any role for monoamine oxidase participation in the mutagenic activation of these compounds must be subsequent to an initial conversion of these compounds to their respective secondary amines.The carcinogenic effect of N-nitrosodialkylamines is known to be expressed by metabolic conversion of these amines to reactive intermediates. These reactive intermediates would then interact with DNA to form O-alkyl bases (1), and this alkylation leads to a series of events culminating in carcinogenesis. It is thus of basic interest to identify the enzyme system involved that converts N-nitroso compounds to their activated, carcinogenic forms. Once identified, suitable inhibitors of the activating enzyme system could be used to prevent expression of the carcinogenic activity of the N-nitrosamines.An extensive literature exists to show that N-nitrosodimethylamine (dimethylnitrosamine) can be demethylated by the cytochrome P-450 system to form formaldehyde (2); however, recent studies have shown that the action of mammalian cytochrome P-450 on dimethylnitrosamine does not result in the production of mutagenic species as monitored in the Ames test (3). These results suggested that the mutagenic activation of N-nitrosodialkylamines is effected by an enzyme system distinct from the cytochrome P-450 system.Recent studies in vivo and in vitro (4)(5)(6) Taken together, these studies suggest a role for MAO in the hepatic activation of N-nitrosodialkylamines to a mutagenic form. If MAO were the primary enzyme involved, then N-nitrosodialkylamines might be expected to be reasonable substrates for the purified enzyme. This study was undertaken to investigate this possibility. As shown in this paper, several N-nitrosodialkylamines are shown not to be substrates for MAO, thus demonstrating that the primary step in the metabolic activation of N-nitrosodialkylamines must be catalyzed by another enzyme. METHODS AND MATERIALSMAO was isolated from bovine liver mitochondria according to the method published by Salach (7). The specific activity of the preparation was in good agreement with that published. Rates of benzylamine oxidation were measured spectrophotometrically by following the increase in absorbance at 250 nm due to benzaldehyde formation as published by Tabor et al. (8). The rates of oxygen reduction were determined by using a Yellow Springs oxygen electrode and monitor in conjunction with a laboratory-built voltage suppr...

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“…MAO was isolated from bovine liver mitochondria according to the method published by Salach (7). The specific activity of the preparation was in good agreement with that published.…”

Section: Methodssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 99%

N-nitrosodialkylamines do not function as substrates for liver monoamine oxidase.

Edmondson¹,

Bruice²

1985

Proc. Natl. Acad. Sci. U.S.A.

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“…Monoamine oxidase A from human placental mitochondria [14] and monoamine oxidase B from ox liver mitochondria [15,16] were isolated by procedures described in the literature. Their activities were determined spectrophotometrically at 30°C by using strict initial-rate measurements, the former with kynuramine, and the latter with benzylamine as substrate, as in previous work [3].…”

Section: Methodsmentioning

confidence: 99%

Mechanism-based inactivation of monoamine oxidases A and B by tetrahydropyridines and dihydropyridines

Krueger

McKeown

Ramsay

et al. 1990

Biochemical Journal

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I-Methyl-4-phenyl-1 ,2,3,6-tetrahydropyridine (MPTP) and its primary oxidation product, l-methyl-4-phenyl-2,3-dihydropyridinium (MPDP+), are mechanism-based inhibitors of monoamine oxidases A and B. The pseudo-first-order rate constants for inactivation were determined for various analogues of MPTP and MPDP+ and the concentrations in all redox states were measured throughout the reaction. Disproportionation was observed for all the dihydropyridiniums, but non-enzymic oxidation was insignificant. The dihydropyridiniums were poor substrates for monoamine oxidase A and, consequently, inactivated the enzyme only slowly, despite partition coefficients lower than those for the tetrahydropyridines. For monoamine oxidase B, the dihydropyridiniums were more effective inactivators than the tetrahydropyridines. Substitutions in the aromatic ring had no major effect on the inactivation of monoamine oxidase B, but the 2'-ethyl-and 3'-chloro-substituted compounds were very poor mechanism-based inactivators of monoamine oxidase A. It is clear that both oxidation steps can generate the reactive species responsible for inactivation.

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“…MAO B was purified from bovine mitochondria according to Salach [19]. Antisera to MAO B were raised in New Zealand white rabbits as reported [lo] except that no injections were made in the feet.…”

Section: Other Methodsmentioning

confidence: 99%

The in vitro insertion of monoamine oxidase B into mitochondrial outer membranes

1988

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Bovine monoamine oxidase (MAO) B has been synthesized in vitro using a reticulocyte lysate translation system directed by bovine liver poly(A)+ RNA. The newly synthesized enzyme apparently lacks a cleavable N‐terminal extension, but MAO B is readily incorporated into mitochondria or isolated mitochondrial outer membranes prepared from rat liver. ATP is not required for the binding of the newly synthesized enzyme to the outer membranes, but is necessary for the insertion of MAO B into these membrane vesicles. The ATP is not required to generate a mitochondrial membrane potential as assembly occurs under conditions that preclude either the formation or the maintenance of the potential. MAO B will bind to but not become incorporated into outer membrane vesicles which have been treated with trypsin, suggesting that the insertion of MAO B also depends on protein factors present on the outer membranes.

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Monoamine oxidase from beef liver mitochondria: Simplified isolation procedure, properties, and determination of its cysteinyl flavin content

Cited by 141 publications

References 33 publications

N-nitrosodialkylamines do not function as substrates for liver monoamine oxidase.

N-nitrosodialkylamines do not function as substrates for liver monoamine oxidase.

Mechanism-based inactivation of monoamine oxidases A and B by tetrahydropyridines and dihydropyridines

The in vitro insertion of monoamine oxidase B into mitochondrial outer membranes

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