It is thought that up to 30 E1 and 6 E3 enzymes are present, although the exact number of molecules can vary in vivo and often reflects the metabolic requirements of the tissue in question.
En eucariotas, crese que están presentes ata 30 copias de E1 e 6 de E3, aínda que o número exacto de moléculas pode variar in vivo e a miúdo reflicte os requirimentos metabólicos do tecido en cuestión.