J Neural Transm (2007) 114: 743–746 DOI 10.1007/s00702-007-0681-0 Printed in the Netherlands Hydrazine and amphetamine binding to amine oxidases: old drugs with new prospects P. Knowles 1 , C. Kurtis 1 , J. Murray 1 , C. Saysell 1 , W. Tambyrajah 1 , C. Wilmot 1 , M. McPherson 1 , S. Phillips 1 , D. Dooley 2 , D. Brown 2 , M. Rogers 2 , M. Mure 3 1 Astbury Centre for Structural Biology, University of Leeds, Leeds, UK 2 Chemistry Department, Montana State University, Bozeman, MT, USA 3 Chemistry Department, University of California, Berkeley, USA Received: October 3, 2006 = Accepted: November 1, 2006 = Published online: April 4, 2007 # Springer-Verlag 2007 Summary Tranylcypromine (TCP), an amphetamine, is a reversible inhib- itor of copper-containing amine oxidases. We have solved the structure of the complex of TCP with the amine oxidase from E. coli (ECAO) and shown that only the (þ)-enantiomer of TCP binds. Kinetic studies on 2-phen- ylethylamine and TCP binding to wild-type ECAO and mutational variants fully support the model in which binding of the protonated amine is the first step in the catalytic cycle. Hydrazines are irreversible inhibitors of copper-containing amine oxi- dases. Binding of hydrazines leads to an adduct (‘‘Adduct 1’’) with a chro- mophore at 430 nm which converts at higher pH to another adduct (‘‘Adduct 2’’) with a chromophore at 520 nm. We have determined the structures of Adduct 1 and 2 for 2-hydrazinopyridine reacted with ECAO. It has been found that Adduct 1 corresponds to the hydrazone and azo tautomers whilst Adduct 2 corresponds to the azo tautomer coordinated to the active site copper. The implications of these results in developing more specific drugs are discussed. Keywords: Amine oxidase, 2-hydrazinopyridine (2-HP), 2-phenylcyclo- propylamine (TCP), pH, trihydroxyphenylalanine (TPQ) Introduction Tranylcypromine (2-phenylcyclopropylamine, TCP), an amphetamine, is used in the treatment of depression where it acts through reversible inhibition of flavin-containing amine oxidases in the brain. TCP is administered as the racemic mixture of the two trans enantiomers, 1S,2R-trans- 2-phenylcyclopropylamine ((þ)-TCP) and 1S,2R-trans-2- phenylcyclopropylamine (()-TCP) (Mallinger et al., 1990). Multiple side effects of TCP administration have been reported and this has led to the development of new anti- depression drugs, for example the serotonin re-uptake inhib- itors. It has also been reported that there are differential effects when the enantiomeric forms of TCP are adminis- tered with (þ)-TCP being 10  more potent as an MAO inhibitor than the racemic mixture whilst ()-TCP is 4  more effective as an inhibitor of catecholamine uptake (Moises and Beckmann, 1981; Weber-Grandke et al., 1993). Some of the side effects of TCP administration could be due to inhibition of copper-containing amine oxidases. A BLAST analysis of the human genome data base reveals three copper-containing amine oxidases and five lysyl oxidase-like proteins, all of which would be inhibited by amphetamines (and hydrazines). Medical interest in cop- per-containing amine oxidases is growing following the discoveries that Vascular Adhesion Protein-1 (VAP-1), a protein involved in leukocyte trafficking and glucose up- take, is an amine oxidase (Jalkanen and Salmi, 2001) and that the ras-recision gene product is a lysyl oxidase (Kenyon et al., 1991). Thus it is of interest to study how TCP inhibits copper-containing amine oxidases since this might contribute to the development of drugs which dif- ferentially act on the different amine oxidases present in human tissues. Hydrazines are very effective antidepression drugs where they act as irreversible monoamine oxidase inhibitors. Their administration leads to sleep disturbance and pre- scription of barbiturates to overcome this problem resulted Correspondence: Peter F. Knowles, Astbury Centre for Structural Biology, University of Leeds, Leeds LS 2 9JT, UK e-mail: knowles.shadwell@ntlworld.com