[Catalytic properties and stability of catalase in reversed micelles of aerosol OT in octane]. / Kataliticheskie svoistva i stabil'nost' katalazy v obrashchennykh mitsellakh aérozolia OT v oktane.

The catalytic function of catalase and its peroxidatic activity during tetramethylbenzidine (TMB) oxidation by cumene hydroperoxide were studied in reversed micelles of Aerosol OT (AOT) in octane relative to the [H2O]/[AOT] ratio and the initial catalase concentration. The optimum conditions permitting to retain the catalytic activity of the enzyme and its ability to induce peroxidation of TMB, were found. The catalytic function of the enzyme was shown to be dependent on its concentration in AOT micelles. The catalase stability monitored by the catalytic reaction and the decrease of the Soret band were analyzed. Both processes have two phases differing by the rate constants of the pseudo-first order. The catalase inserted into AOT micelles is characterized by the high stability as compared to other hemoproteins (cytochrome P-450, myoglobin, hemoglobin, peroxidase) under identical conditions.

[Peroxidase activity of catalase modified by progesterone]. / Peroksidaznaia aktivnost' katalazy, modifitsirovannoi progesteronom.

Catalase conjugates with 3, 7, 9 and 42 progesterone molecules were obtained by the reaction between the enzyme and N-oxy-succinimide ether of 3-0-carboxymethyloxime of progesterone. The enzyme modified by 42 progesterone molecules is effective in o-dianisidine oxidation by hydrogen peroxide and has a kcat/KM value of 512 M-1 s-1. The catalase conjugates with 3, 7 and 9 progesterone molecules exhibit a high activity during o-dianisidine oxidation by cumene hydroperoxide. The activity of conjugates is higher than that of the native non-modified enzyme in the same reaction. The maximum effectiveness was observed for catalase modified by 7 progesterone molecules. This conjugate is characterized by kcat/KM of 99,000 M-1 s-1 at 30 degrees C. The effect of the degree of enzyme modification on the kinetic parameters of o-dianisidine oxidation by H2O2 and cumene hydroperoxide is discussed.

[Peroxidase activity of succinylated catalase]. / Peroksidaznaia aktivnost' suktsinilirovannoi katalazy.

The catalase succinylation by succinic anhydride excess results in an almost complete dissociation of the enzyme into subunits possessing no catalase activity. The catalase subunits show the peroxidatic activity on o-dianisidine oxidation. The oxidation kinetics of this substrate by the succinylated enzyme was studied at various temperatures. The activation energy for this process is 10.1 kcal/mole. Within the temperature range of 31-65.5 degrees, the succinylated enzyme thermostability was studied by monitoring the peroxidatic activity decrease upon o-dianisidine oxidation. The activation energy for the succinylated catalase thermoinactivation equals to 15.5 kcal/mole. The peroxidatic activity of catalase subunits obtained by enzyme succinylation and acidic solution treatment was compared to that of horseradish peroxidase in the oxidation of the same substrate, i.e., o-dianisidine.

[Peroxidase activity of catalase with respect to aromatic amines]. / Peroksidaznaia aktivnost' katalazy po otnosheniiu k aromaticheskim aminam.

The catalase dissociation into subunits has been studied at pH less than 3.5 and greater than 11.0. This process is characterized by pseudo-first order rate constants, depending on the initial concentrations of the enzyme and H+. At pH 2.85, the steady-state kinetics of five aromatic amines oxidation by catalase monomers has been studied for orthodianisidine (o-DA), 3,5,3',5'-tetramethylbenzidine (TMB), ortho- and para-phenylene diamine (p-PDA) and 5-aminosalycilic acid. The optimal substrates for catalase in acidic solutions are o-DA, TMB and p-PDA. A comparison has been carried out for the catalase peroxidative activity, and the catalytic characteristics of horseradish peroxidase in the oxidation of the same substrate. The mechanisms of peroxidatic amines oxidation by catalase and horseradish peroxidase are discussed.