A recombinant flavocytochrome b2 (FCb2), comprising a mature FCb2 peptide sequence of a native FCb2, or a functionally active variant of said mature FCb2 peptide sequence, wherein the N-terminus of said mature FCb2 peptide sequence consists of a truncated signal peptide sequence replacing the native signal peptide sequence, and wherein said truncated signal peptide sequence is of the following structure from N- to C-terminus: i. a methionine; ii. optionally a tag sequence; iii. an amino acid sequence of a length of 0-9 amino acids of the native signal peptide sequence, corresponding to the amino acid sequence up to 9 amino acids directly upstream of the I/L/V-x-N/A/L motif of the native signal peptide sequence of FCb2; and iv. the I/L/V-x-N/A/L motif, which can be of number 0, 1, or can be partially truncated, wherein if the number is 0 or the I/L/V-x-N/A/L is partially truncated, the length of the amino acid sequence of iii. is 0, wherein the amino acid sequence of said recombinant FCb2 is different from SEQ ID NO: 145.