Methionine residues in the A1A2A3 region of VWF. The A1A2A3 region of VWF contains 14 methionine residues, 4 each in the A1 and A3 domains and 6 in the A2 domain, including M1606 at the ADAMTS13 cleavage site. Methionine residues are the amino acids most susceptible to oxidation by HOCl.