INACTIVATION KINETICS OF HORSERADISH-PEROXIDASE IN ORGANIC-SOLVENTS OF DIFFERENT HYDROPHOBICITY AT DIFFERENT WATER CONTENTS

The thermal stability of horseradish peroxidase suspensions was studie d in three organic solvents of different hydrophobicity (dodecane, oct ane, and I-octanol) at three different water contents (14.1, 55.3 and 256.2 mg water g(-1) dry protein). In these conditions, the enzyme is much more stable than in aqueous solutions (inactivation temperatures were in the range of 125-150 degrees C). The enzyme showed a similar s tability when in the presence of organic solvents, compared to the enz yme in a solid matrix without organic solvents with the same water con tent. The inactivation kinetics was well described by assuming the exi stence of two iso-enzymes, both inactivating according to a first orde r model. The lowest value for the z-value of both fractions (around 15 degrees C) was obtained at the higher water content studied. The use of solvent and water content variables should be adequate to develop t ime-temperature integrators to monitor thermal processes at 100-140 de grees C.