Method for enzymatically producing maytansinol

A method for producing maytansinol, which comprises enzymatically producing maytansinol from an ansamitocin species with:

• (i) a protein consisting of the amino acid sequence of SEQ ID NO:
• 12;
• or
• (ii) a protein consisting of an amino acid sequence having an identity of at least 90% to the amino acid sequence of SEQ ID NO:
• 12, wherein:
• amino acids corresponding to the positions 66 to 68 are DLL or AGA, amino acids corresponding to the positions 139 to 141 are GPF, amino acids corresponding to the positions 146 to 148 are LSS or LSP, amino acids corresponding to the positions 247 to 249 are LHT, amino acids corresponding to the position 322 to 324 are HSX or ASX (where X is Q, K, E, or M), amino acids corresponding to the positions 374 to 376 are QSX (where X is H, R, D, or Q), and amino acids corresponding to the positions 443 to 445 are GNP, and
• having an activity for catalyzing a reaction of producing maytansinol from an ansamitocin species;
• and
• wherein the protein (i) or (ii) is heterologously expressed.