The application of temperature-sensitive polymer (PNIPAAm) for the renaturation of beta-lactamase from inclusion bodies was investigated. It was observed that PNIPAAm was more effective than PEG in enhancing protein renaturation. At a concentration of 0.1%, PNIPAAm improved the yield of beta-lactamase activity by 41% from 46.5 to 65.4 IU/mL, compared to 26% with PEG from 46.5 to 58.7 IU/mL. Kinetic study indicated that PNIPAAm did not significantly affect the initial rate of protein renaturation but did increase final activity yield. In the presence of PEG and PNIPAAm, the activity yields increased with temperature, indicating that hydrophobic interactions between denatured protein and polymer molecules contributed to the enhanced protein renaturation with polymers. The sequential addition approach, aiming at enhancing protein renaturation by reducing local protein concentration during renaturation, was also shown effective in enhancing protein renaturation, especially in the presence of polymers. With the sequential addition approach, the activity yield was increased by 60.5% from 46.5 to 74.6 IU/mL with PNIPAAm. Similar behavior was also observed with PEG. PNIPAAm exhibited similar behavior as PEG on the renaturation of beta-lactamase in terms of temperature effect and concentration effect, indicating that the mechanism for enhanced protein renaturation for the two polymers might be similar. PNIPAAm exhibits a lower critical solution temperature (LCST) of 32 degrees C and can be effectively separated from aqueous solution and recycled. A protein renaturation process employing PNIPAAm, which offers the advantages of en ha need renaturation efficiency, mini mum loss of protein aggregates, and ease of polymers recycling, was proposed. (C) 2000 John Wiley & Sons, Inc.