The present invention relates to a variant of an alpha-keto acid dependent enzyme catalyzing the oxidative decarboxylation of an alpha-keto acid having an amino acid sequence varying from that of a precursor alpha-keto acid dependent enzyme catalyzing the oxidative decarboxylation of an alpha-keto acid, said precursor enzyme comprising

- a motif (A) X₁X₂X₃X₄(X)_nFGX₅X₆NX₇X₈X₉X₁₀X₁₁, wherein X₁ is serine, X₂ is an amino acid residue selected from the group consisting of threonine, lysine, isoleucine, arginine and glutamine, X₃ is valine or alanine and X₄ is an amino acid residue selected from the group consisting of valine, methionine and isoleucine, X₅ and X₆ are independently any amino acid residue, X₇ is isoleucine or phenylalanine, X₈ is an amino acid residue selected from the group consisting of lysine, glutamine, arginine and threonine, X₉ is an amino acid residue selected from the group consisting of alanine, serine and glycine, X₁₀ is leucine or isoleucine, X₁₁ is tyrosine or phenylalanine, X is any amino acid residue, and n is an integer between 100 and 150, and

- a metal ion binding motif (B) H(X₁₂)_mH(X₁₃)_oE, wherein X₁₂ and X₁₃ are independently any amino acid residue, m and o are independently an integer between 70 and 90,



wherein amino acid residue X₁ and/or amino acid residue X₃ within motif (A) of the variant is an amino acid residue having a molecular volume of more than 150 ų and/or amino acid residue X₁₁ within motif (A) of the variant has an amino acid residue having a molecular volume of less than 120 ų.