Study of the (S)-hydroxynitrile lyase from Hevea brasiliensis: mechanisticimplications

Investigations of the (S)-selective hydroxynitrile lyase from Hevea brasili ensis were performed by electrospray mass spectroscopy, H-1-NMR and with an enzyme activity assay. For the trans-cyanohydrin reaction (transcyanation) a two step reaction could be established. The results furthermore indicate a fast deactivation of the enzyme at low pH and a strong substrate depende nce of its stability. They rule out an enzyme-HCN complex or a covalently b ound carbonyl compound. Therefore the earlier postulated reaction intermedi ate as well as the proposed action of the catalytic triad have to be reeval uated. The calculated molecular mass could be confirmed by mass spectroscop y. (C) 1999 Elsevier Science B.V. All rights reserved.