Catalase molecular activity

Rate Constants kV2 foe the Formation of Compound I from H202 and Selected Peroxidases or Catalases and for Non-Fenton Peroxidase- or Catalase-Related Activation of H202 Such as k by the Most Reactive Low-Molecular Weight Ieon(III) Complexes in Water... 

The molecular masses of heme catalases are usually significantly higher as compared with peroxidases. If expressed in Lg-1s-1, rate constants for the Fem-TAML activators when compared with catalase from beef liver, which has a molecular weight 250,000 gmol-1 (Table IV, entry 13) (89), look very impressive, viz. 17 L g 1 s-1 for 11 vs. 22 L g 1 s 1 for the enzyme. Nevertheless, the catalase-like activity of the Fem-TAML activators can be suppressed by the addition of electron donors -it is negligible in the presence of the substrates tested in this work. In Nature, catalases display only minor peroxidase-like activity (79) because electron donors bulkier than H202 cannot access the deeply buried active sites of these massive enzymes (90). The comparatively unprotected Fem-TAML active sites are directly exposed to electron donors such that the overall behavior is determined by the inherent relative reactivity of the substrates. 

The action of catalase is very fast, almost 104 times faster than that of peroxidases. The molecular activity per catalytic center is about 2 x 105 s-1. 

The true physiological role of cytochrome c peroxidase in yeast is yet to be established. It may serve as a part of the systems which prevent intracellular accumulation of harmful hydrogen peroxide. It would be of interest to know if cytochrome c peroxidase is synthesized concurrently with or in competition with the production of other peroxide-decomposing systems such as catalase. Although cytochrome c peroxidase is present in mitochondria of aerobically grown yeast in a concentration comparable to that of cytochrome oxidase (19) and possesses an extremely high molecular activity (fcj = 10 sec ) toward yeast ferrocytochrome c (17), it has not been unequivocally shown that ferrocytochrome c is a true substrate of this enzyme. 

The catalase like activity was tested with (48) as catalyst From the results it is evident that the polymer bond in phthalocyanine led to a lower activation ener due to h%her concentration of not aggregated active centers than with low molecular jAthalocy-anines. Continuous flow experiments in a column show that (48) keeps 60% of its original activity. The polymer is more stable than the low molecular phthalocyanine. 

The catalatic activity was inhibited by CN", N and NH2OH. Some enzymatic properties of the catalase are summarized in Table 1. value and molecular activity were similar to those of typical catalases. 

When the molecular weight of a pure enzyme is known it is possible to determine the molecular activity or turnover number,i.e. the number of molecules of substrate transformed per minute per molecule of enzyme. These are usually of the order of several thousand, although acetyl cholinesterase has a value of 950 000 and catalase 5 000 000. 

One of the important consequences of neuronal stimulation is increased neuronal aerobic metabolism which produces reactive oxygen species (ROS). ROS can oxidize several biomoiecules (carbohydrates, DNA, lipids, and proteins). Thus, even oxygen, which is essential for aerobic life, may be potentially toxic to cells. Addition of one electron to molecular oxygen (O,) generates a free radical [O2)) the superoxide anion. This is converted through activation of an enzyme, superoxide dismurase, to hydrogen peroxide (H-iO,), which is, in turn, the source of the hydroxyl radical (OH). Usually catalase... 

Henkle-Duhrsen, K., Eckelt, V.H., Wildenburg, G., Blaxter, M. and Walter, R.D. (1998) Gene structure, activity and localization of a catalase from intracellular bacteria in Onchocerca volvulus. Molecular and Biochemical Parasitology 96, 69-81. 

Fig. 3.1 The molecular structure of heme b (also called protoporphyrin IX), the active center of myoglobin, hemoglobin, catalases, and peroxidases, among other heme proteins. 

Bacterial SODs typically contain either nonheme iron (FeSODs) or manganese (MnSODs) at their active sites, although bacterial copper/zinc and nickel SODs are also known (Imlay and Imlay 1996 Chung et al. 1999). Catalases are usually heme-containing enzymes that catalyze disproportionation of hydrogen peroxide to water and molecular oxygen (Eq. 10.2) (Zamocky and Koller 1999 Loewen et al. 2000). 

Milk catalase is a haem protein with a molecular weight of 200 kDa, and an isoelectric pH of 5.5 it is stable between pH 5 and 10 but rapidly loses activity outside this range. Heating at 70°C for 1 h causes complete inactivation. Like other catalases, it is strongly inhibited by Hg2+, Fe2+, Cu2+, Sn2+, CN- and NOJ. 

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