Studies on the mechanism of action of plasma amine oxidase

Journal of Pharmacy and Pharmacology

Callingham

1992

The effects were examined of four metabolites of the anticancer agent, procarbazine (N-isopropyl-alpha-(2-methyl hydrazino)-p-toluamide hydrochloride) on semicarbazide-sensitive amine oxidase (SSAO) and monoamine oxidase-A and -B (MAO-A and -B) activities in rat brown adipose tissue and liver homogenates, respectively. Azoprocarbazine (AZO) and monomethylhydrazine (MMH) inhibited selectively the deamination of benzylamine by SSAO, when compared with their effects on MAO activities. The IC50 values against SSAO, of 32.7 nM (AZO) and 7.0 nM (MMH), were more than three orders of magnitude lower than those exhibited against MAO. Neither isomer of azoxyprocarbazine was an effective inhibitor of rat amine oxidase activities. The inhibition of SSAO by AZO was reversed very slowly by dialysis, in contrast to results seen for MMH. The non-competitive kinetics of MMH and the ability of B24, a rapidly reversible SSAO inhibitor, to protect SSAO against inhibition by MMH are consistent with the view that this compound binds to the enzyme cofactor at, or near, the active site.

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Section: Discussionsupporting

confidence: 85%

Effects In-vitro of Procarbazine Metabolites on Some Amine Oxidase Activities in the Rat

Journal of Pharmacy and Pharmacology

Callingham

1992

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“…Kinetic experiments showed the interaction between SSAO and procarbazine to be non-competitive in nature. It is thought that hydrazine derivatives can interact with a Qrbonyl group on the cofactor, perhaps resulting in the formation of a diimide (Suva & Abeles 1978), and it is Probable that procarbazine acts in a similar fashion. Our results suggest that in the first instance, affinity of procarbatine for the enzyme is low.…”

Section: Discussionmentioning

confidence: 99%

“…It is likely that the cofactors of SSAO isolated from various sources are situated at the active sites of these enzymes (Suva & Abeles 1978;Hartmann & Klinman 1990Janes et a1 1990;Janes & Klinman 1991). Thus the ability of benzylamine to afford substantial protection against inhibition by procarbazine suggests that, in rat brown fat, the cofactor is at the active site.…”

Section: Discussionmentioning

confidence: 99%

Characteristics of Procarbazine as an Inhibitor In-vitro of Rat Semicarbazide-sensitive Amine Oxidase

Journal of Pharmacy and Pharmacology

Callingham

et al. 1992

Procarbazine (N-isopropyl-alpha-(2-methyl hydrazino)-p-toluamide hydrochloride) inhibited more powerfully the deamination of benzylamine by semicarbazide-sensitive amine oxidase (SSAO) of rat brown adipose tissue than the deamination of 5-hydroxytryptamine and benzylamine by rat liver monoamine oxidase-A or -B activities, respectively. Inhibition of SSAO, but not monoamine oxidase, was time-dependent. Use of metabolic inhibitors, and an enzyme dilution technique, suggested that any conversion of procarbazine to an active species must be as a result of the action of SSAO itself and not of any other enzyme. The non-competitive kinetics and the time-dependence of inhibition were indicative of a suicide interaction between procarbazine and SSAO. The slow reversal of inhibition by dialysis was evidence in favour of the involvement of tight binding, rather than covalent bonding. High concentrations of benzylamine afforded the enzyme significant protection from the action of procarbazine, indicating that the interaction is at or near the active site. If the properties of procarbazine, evident in in-vitro studies, are retained in-vivo, these data suggest that procarbazine might be suitable for the examination of SSAO activities, both in-vivo and ex-vivo.

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“…Substrate concentrations were chosen with respect to literature used for benzaldehyde (25). In parallel studies, cuvettes contained 33 ml mitochondria preparation, 133 K m values for tyramine metabolism by MAO in rat liver isolated mitochondria (24).…”

Section: Selective Measurement Of Mao-a and Mao-bmentioning

confidence: 99%

A Continuous Spectrophotometric Assay for Monoamine Oxidase and Related Enzymes in Tissue Homogenates

Analytical Biochemistry

Baker

et al. 1997

222

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