( College of Biosystem Engineering and Food Science, Zhejang University, Hangzhou 310029, China;
¹ PLA Centre of Infectious Diseases, Guangzhou Airforce Hospital, Guangzhou 510620, China )

Abstract To investigate the modification of recombinant human augmenter of liver regeneration (rhALR) by the urea in purification processes and the biological activity of rhALR and modified rhALR, the molecular weight of proteins and tryptic peptides were determined by matrix-assisted laser desorption time of flight mass spectrometry (MALDI-TOF-MS), and the biological activity of rhALR and modified rhALR was also observed by in vivo experiments. A 30 kD homodimer of rhALR was purified under denaturing conditions. The molecular weight of rhALR is 30 780 if urea was used to denature the inclusion bodies; when the denaturant was guanidine hydrochloride, the molecular weight of rhALR was 30 087. The results of MALDI-TOF-MS of digested rhALR that have been modified by urea showed that peptides that contained lysyl were 43 larger than the theoretical value. Proteins purified by different processes were all able to promote the survival rate of CCl4-intoxicated mice. It could be concluded that cyanate, the cleavage product of urea, could react with the ε-amino group of lysyl in rhALR, and the modified rhALR had the same biological activity as natural rhALR.