Animal-free Recombinant Human pro-IGF-II is expressed in human 293 cells as a monomeric glycoprotein with an apparent molecular mass of 25 kDa. Glycosylation contributes to stability in cell growth media and other applications. IGF-II expressed in E. coli is typically 7.5 kDa and nonglycosylated. This cytokine is produced in a human cell expression system with serum-free, chemically defined media.