Kinetics and stereospecificity of the lysyl oxidase reaction

The structural specificity of amine oxidation by lysyl oxidase was investigated using kinetic and NMR spectroscopic analyses. Substrate efficiency increased with increasing molecular distance from the alpha-carbon of the aromatic moiety substituted on the aliphatic chains of a series of primary amines. The p-hydroxyl substituent of p-hydroxybenzylamine significantly increased kcat over that of benzylamine, whereas this was not the case when tyramine and phenethylamine were compared. Direct spectrophotometric measurement of p-hydroxybenzaldehyde formation yielded burst kinetics, the second, slower phase of which was eliminated under anaerobic conditions. Thus, enzyme reoxidation is the more rate-limiting of the two half-reactions catalyzed with this substrate by this ping-pong enzyme. 1H NMR spectroscopy of the alcohol reductively derived from the aldehyde product of the lysyl oxidase-catalyzed oxidation of deuterated tyramine indicated that the pro-S but not the pro-R alpha-deuteron was catalytically abstracted. Moreover, lysyl oxidase catalyzed solvent exchange of protons at the C-2 position. Such stereospecificity and proton exchange uniquely differentiates lysyl oxidase from all but an aortic semicarbazide-sensitive amine oxidase among the pro-S-specific copper-dependent amine oxidases analyzed thus far.