The Stereochemistry of Enzymic Reactions at Prochiral Centres

Abstract

<p>The steric course of decarboxylation of L-ornithine to yield putrescine, catalysed by L-ornithine decarboxylase (E.C. 4.1.1 17) of E. coli, and of L-arginine to yield agmatine, catalysed by L-arginine decarboxylase (E.C. 4.1.1.19) of E. coli, is investigated by deuterium labelling. Replacement of the carboxyl group by a solvent derived proton occurs with retention of configuration in each case.</p> <p>In conflict with an earlier report, incubation of cadaverine in deuterium oxide in the presence of L-lysine decarboxylase (E.C. 4.1.1.18) of B. cadaveris did not lead to entry of deuterium into the α-position of cadaverine. Likewise, L-ornithine decarboxylase did not catalyse exchange of the α-hydrogen of putrescine, nor did L-arginine decarboxylase catalyse such an exchange in agmatine.</p> <p>The stereochemistry of hydrogen abstraction in the conversion of cadaverine into 'Δ'-piperidine, of putrescine into Δ'-pyrroline, and of agmatine into 4-guanidinobutanal, catalysed by hog kidney diamine oxidase (E.C. 1.4.3.6) is investigated. The Si-hydrogen from C-1 of the substrate is removed while the Re-hydrogen from C-1 of the substrate is maintained at the Sp² carbon atom of each of the products.</p> <p>The diamine oxidase catalysed oxidative deamination of cadaverine takes place without detectable isotope effect, while an intramolecular primary hydrogen-deuterium isotope effect (kHsi./kDsi = 4) is observed in the diamine oxidase catalysed oxidation of putrescine.</p>