The present invention relates to newly identified mutants of (R)-selective hydroxynitrile lyase enzyme (R-HNL), in particular variants of Pa HNL (hydroxynitrile lyase isoenzyme 5 of Prunus amygdalus) which are stable at very low pH, i.e. at pH around 2.5 and lower. In particular, the present invention provides nucleic acids encoding said mutant enzymes, recombinant microorganisms and their use for industrial applications.
