Enzyme immobilization offers numerous advantages in terms of practical applications spanning biosensors to reactors. Bovine liver catalase (BLC [EC 1.11.1.6]) was immobilized in tetraethoxyorthosilicate (TEOS) based sol-gels. TEOS sol-gels were found to be suitable for entrapping BLC with a high degree of immobilization. Kinetic constants for the catalatic mode of action of the immobilized enzyme were determined. Immobilized BLC retained less than 1% catalatic but 50% peroxidatic activity compared to its free counterpart. Addition of various additives did not improve the catalatic performance. Structural integrity of the immobilized enzyme and availability of active sites was confirmed by UV-vis-spectroscopy suggesting that the relatively low catalatic activity is due to effects of the sol-gel matrix on oxygen yielding reactions and dissolution into aqueous media. These data also imply that there may be significant mass transfer resistance due to the matrix depending on the nature of the substrate and product. Spectroscopic studies also indicated that the sol-gel matrix protects the catalase from formation of the inactive compound II. Heat inactivation studies showed a significantly improved thermostability of the immobilized preparation with a doubling of the inactivation energy when compared to the free enzyme. Sol-gel immobilized BLC was found to be stable for 17 consecutive reactor batch cycles with no apparent loss in activity.(c) 2005 Elsevier Inc. All rights reserved.