Biol. Pharm. Bull., 33(7),1253-1255, July 2010


Amino Group PEGylation of Bovine Lactoferrin by Linear Polyethylene Glycol-p-nitrophenyl Active Esters

Kanako KATO, Naomi TAMAKI, Yoshiki SAITO, Tomohito FUJIMOTO, and Atsushi SATO*

School of Bioscience and Biotechnology, Tokyo University of Technology; 1404-1 Katakura, Hachioji, Tokyo 192-0982, Japan. * To whom correspondence should be addressed. e-mail:

PEGylation, the covalent attachment of polyethylene glycol (PEG) to pharmaceutical proteins, is regarded as an extremely useful procedure to generate protein drugs with intensified therapeutic properties. We examined the amino group modification of bovine lactoferrin (bLF) with linear PEG-p-nitrophenyl active esters. At pH 5.0, we specifically observed the formation of mono-PEGylated bLF in high yields. PEG-conjugation reactions advanced slowly and reached a steady state by 48 h in a buffer at pH 5.0. The hydrolysis half-lives of 5-kDa and 30-kDa PEG-p-nitrophenyl active esters at pH 5.0 were estimated to be approximately 117 and 136 h, respectively. The slow reaction and hydrolysis rates of PEG-p-nitrophenyl active esters may contribute to the formation of mono-PEGylated bLF that could not be obtained by PEGylation with linear N-hydroxysuccinimide (NHS) activated PEG.

Key words p-nitrophenyl active ester; polyethylene glycol; pH; kinetic; lactoferrin; hydrolysis