Pectin was attached to ethylenediamine-activated carbohydrate moieties of invertase using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling agent. The modified enzyme retained 57% of the original activity and contained 2.7 mol polymer per mol holoenzyme. Its optimum temperature was increased by 8 degrees C and its thermostability by 7.3 degrees C. The half-life at 65 degrees C was increased from 5 min to 2 days. The enzyme stability was enhanced by 33% at pH 2.0, and also by 27% at pH 12.0. The conjugate retained about 96% of its initial activity after 3 h incubation in 6 M urea.