The effect of three different sugars, sorbitol, melezitose and trehalose, on horseradish peroxidase A₁, HRPA₁ thermostability was evaluate under different environmental conditions, namely, ionic strength and pH.

The ionic strength range studied varied from 25 to 125mM in phosphate buffer, pH 6.5. At 75 and 125mM, the addition of 1M trehalose improved 20 and 18 fold, respectively, the stability of the enzyme. With 0.5M melezitose the stability of the enzyme improved 12 fold at 75mM while at 125mM an increase of 7 fold was observed. In the case of sorbitol, a maximum of 5 fold improvement was evidenced.

The effect of the additives on HRPA₁ stability, at different pH values, ranging from 5.5 to 7.5, in 25mM phosphate buffer, was also evaluated. The stabilization by the addition of 1M trehalose was almost the same in the range of pH values studied, varying between 7 and 10 fold. The addition of 1M sorbitol produced an increase of 2 fold in the stability of the enzyme, at the extreme pH values while at pH 6.5 a destabilizing effect was observed.

The stabilization observed in the presence of the three additives depends mainly of the ionic strength of the medium. This protective effect was more pronounced at the extremes values of pH and ionic strength tested.