Biochanical Phammcology. Vol. 27. PP. 1857-1863. @ Pergamon Press Ltd. 1978. Printed in Great Britain. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG A BENZYLAMINE OXIDASE DISTINCT FROM MONOAMINE OXIDASE B-WIDESPREAD DISTRIBUTION IN MAN AND RAT RACHEL LEWINSOHN, K.-HEINRICH B~HM, VIVEITE GLOVER and MERTON SANDLER Bernhard Baron Memorial Research Laboratories and Institute of Obstetrics and Gynaecology, Queen Charlotte’s Maternity Hospital, London W6 OXG, U.K. (Receioed 16 January 1878; accepted 28 February 1978) Abstract-Benzylamine oxidase (BzAO) and monoamine oxidase type B(MAO-B) both selectively catalyse the oxidative deamination of benzylamine (Bz). We define the former as that benzylamine- metabolizing activity insensitive to 4 x lo-’ M deprenyl, a concentration which totally inhibits all forms of MAO. Although both enzymes are widespread in human and rat tissues, their organ distribution differs. Liver and brain show highest MAO-B activity, whilst BzAO activity pre- dominates in aorta and lung. Relatively low BzAO and no MAO-B activity is present in plasma. In the rat, phenylethylamine (PEA) and dopamine (DA) are both substrates for a deprenyl-resistant enzyme with a distribution similar to BzAO, but in man these amines are solely oxidized by MAO. At pH 7.2 the K, of BzAO for benzylamine is 2.2 X lo-’ M in the rat; pn man, it is 1.1 x lo-’ M. The K,,, of MAO-B for benzylamine is 1.0~ lo-‘M in the rat and 5 x lo-’ M in man. Semicarbazide, orocarbazine and carbidooa are ootent inhibitors of BzAO and inhibit it selectively, leaving MAO substantially unaffected. _ Monoamine oxidase (monoamine: O2 oxidoreduc- tase (deaminating) EC 1.4.3.4.) (MAO) is a mito- chondrial flavoprotein enzyme which oxidatively deaminates a wide range of monoamines[l]. Two forms have been distinguished by Johnstonl21, although such a classification is at best approximate[3]; type A selectively deaminates 5- hydroxytryptamine (5-HT); type B prefers phenyl- ethylamine (PEA) and benzylamine (Bz) as substrates[4]. Evidence has also accrued that a different enzyme, benzylamine oxidase (BzAO), is able to catalyse the oxidation of Bz[l]. It is not a flavoprotein, but is copper-dependent [ 11 and may use pyridoxal as cofactor[l]. This enzyme, which has been identified in the blood of many species, has been extensively purified from human plasma and characterized by McEwen[5,6]. It bears a strong resemblance to a Bz-oxidizing activity dis- tinct from MAO-B, which has been sporadically described in tissues as various as bovine aortal71, rat heart[8], rabbit lung[9], rat artery[lOl, and many organs in the pig, particularly in connective tissue [ 111. One of us has recently shown[ 121 that serum BzAO activity is significantly decreased in patients who have sustained severe burns, and in patients with cancer. In an attempt to elucidate the significance of these observations, we decided to embark on a study of BzAO activity and inhibitor sensitivity patterns in human and rat tissues. BzAO can be conveniently distinguished from MAO by selective inhibition with deprenyl, to which MAO-B is particularly sensitive but which inhibits all forms of MAO in higher concentration, leaving BzAO unaffected. Although the Bz-oxidiz- ing MAO-B has aroused greater interest [ 1,8- 10, 13-171, no fully systematic attempt has so far been made to study the distribution of either en- zyme in human or rat tissues. hiATgBIAL.5 AND METAODS Chemicals. Benzylamine hydrochloride methy- lene[‘%] was purchased either from ICN Phar- maceuticals, Inc., Irvine, U.S.A. (sp. act. 12.5 mCi/m-mole), or from Radiochemical Centre Ltd., Amersham, U.K. (sp. act. 56mCi/m-mole). The radiochemical purity of both was 99 per cent. [‘4ClPhenylethalamine, sp. act. 50.98 mCi/m-mole, was purchased from New England Nuclear, Boston, U.S.A., and [‘4C]dopamine, sp. act. 62 mCi/m-mole, from Radiochemical Centre Ltd., Amersham, U.K. The following compounds were kindly donated: deprenyl by Professor J. Knoll, Budapest, by ar- rangement with the Chinoin Co., Budapest; pro- carbazine hydrochloride (Ro 4-6467) and benserazide (Ro 4-4602) by Roche Products Ltd., Welwyn Garden City, U.K.; carbidopa by Merck, Sharp & Dohme Ltd., Hoddesdon, U.K.; and clorgyline by May & Baker Ltd., Dagenham, U.K. Isoniazid, penicillamine, and &amino- propionitrile fumarate (BAPN) were purchased from Sigma Chemical Co., St. Louis, U.S.A., pargyline from Abbott Laboratories, North Chi- cago, U.S.A., and semicarbazide hydrochloride, 99.5 per cent pure (AnalaR grade) from BDH Chemicals, Poole, U.K. Benzylamine, purchased as free base from Sigma London Chemical Co. Ltd., Kingston-upon-Thames, U.K., was converted to its hydrochloride by treatment with hydro- chloric acid, and recrystallized. All other reagents were obtained from commercial sources. Tissues. (a) Rat. Male Wistar rats (200-25Og) were killed by decapitation. Tissues, freed from blood by rinsing in 0.9% saline and drying between layers of tilter paper, were coarsely sliced or minced with scalpel or razor blade, quick-frozen in solid C&(-80”), and either homogenized immediately with 0.1 M sodium phosphate buffer (PH 7.4), BP Vol. 27, No. 14-E