Nat Biotechnol. 2012 Nov;30(11):1143-8. doi:10.1038/nbt.2375

Martell JD, Deerinck TJ, Sancak Y, Poulos TL, Mootha VK, Sosinsky GE, Ellisman MH, Ting AY.

Engineered ascorbate peroxidase as a genetically encoded reporter for electron microscopy.

APEX: a “genetically encodable EM tag that is active in all cellular compartments and does not require light APEX is a monomeric 28-kDa peroxidase that withstands strong EM fixation to give excellent ultrastructural preservation”.