Chemical modification of wheat β-amylase by trinitrobenzenesulfonic acid, methoxypolyethylene glycol, and glutaraldehyde to improve its thermal stability and activity

The amino groups of wheat beta-amylase (WBA) were modified by 2,4,6-trinitrobenzenesulfonic acid (TNBS), 2,4-bis (O-methoxypolyethylene glycol)-6-chloro-s-triazine (mPEG), and glutaraldehyde (GA) to improve its thermal stability and activity. Modification of WBA by 5 mM TNBS, 4.8 mu M mPEG and 11 mM GA improved its T-50 (the temperature at which 50% of its activity is lost after 30 min of incubation) from 47 +/- 1 degrees C to 48 +/- 2, 55 +/- 2, and 54 +/- 2 degrees C, respectively. The catalytic activity of WBA was reduced by 15% and 59% with modification by 5 mM TNBS and 11 mM GA, respectively. In all cases, the enhancement of thermostability of modified WBA was entropically driven. The activity of WBA modified by 4.8 mu M mPEG was enhanced by 39% at 25 degrees C. Therefore, the thermal stability of WBA was significantly improved by modification with mPEG, GA and slightly by TNBS and its catalytic activity was enhanced by mPEG. (C) 2013 Elsevier Inc. All rights reserved.