Kinetic Studies on the Interactions of Mitochondrial Monoamine Oxidase-B of Human and Pure Ox Liver with 2-(Benzylamino) Acetamide

Ramadan, Zakia M. Ben; Tipton, Keith F.; El Deib, Maha M.

doi:10.21608/blj.2016.48189

Kinetic Studies on the Interactions of Mitochondrial Monoamine Oxidase-B of Human and Pure Ox Liver with 2-(Benzylamino) Acetamide

Document Type : Original Article

Authors

¹ Department of Biochemistry, Faculty of Medicine, University of Tripoli-Libya

² Department of Biochemistry, Trinity College, Dublin 2, Ireland

³ Central Laboratory., Zagagazig University, Egypt

10.21608/blj.2016.48189

Abstract

In an attempts to understand more precisely the role of monoamine oxidase (MAO-B) enzyme in the metabolism of the parent anticonvulsant 2-n-pentylaminoacetamide, the benzylamine derivative 2-benzylamino acetamide, also designated as FCE 25692, which used as a substrate and an inhibitor of MAO-B from human liver mitochondria and pure ox liver. The results obtained indicated that FCE 25692 to act as a suicide substrate with apparent Km values of 989 and 950 μM and Vmax values of 0.422 and 93.05 nMol.min-1.mg-1 for human and the purified ox liver MAO-B, respectively, in a way that can explain that it is a better substrate rather than an inhibitor for MAO-B from both species, with partitions ratios of 1062 and 2733 mol of product per mol of enzyme inactivated, for human and ox preparation, respectively. Moreover, the turnover numbers (kcat) and the kcat/Km values confirmed the fact that FCE 25692 is somewhat a better substrate for MAO-B purified from ox liver than from human liver, with kcat/Km values of 40.3 and 17.1 min- 1.mM-1, respectively. The progress curves for the inhibition of MAO-B showed that FCE 25692 has an equipotent time-dependent inhibitor of MAO-B in both preparations. It can be confirmed from the close similar inactivation constant kin and half-life values for MAO-B from both preparations; the t1/2 for the purified ox MAO-B (49.9 min) and for human MAO-B (41.9 min). Despite the fact that benzylamine is a substrate for the semicarbazide-sensitive amine oxidase (SSAO; EC 1.4.3.6), FCE 25692 was found not to be a substrate or an inhibitor for any of that enzyme from ox plasma or lung.

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