Catalase reactivity

The protein factor contains catalase activity and pure catalase reactivates the desaturation. However there is no correlation between the protein factor reactivation capacity on a6 desaturation and catalase activity content. Pure catalase has less reactivation capacity than Sp although it contains many more units of catalase activity. 

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... 

Normally, these reactive species are destroyed by protective enzymes, such as superoxide dismutase in mitochondria and cytosol and catalase in peroxisomes, but if a tissue has been anoxic the respiratory chain is very reduced and reoxygenation allows dangerous amounts to be formed. Muscle also contains significant quantities of the dipeptide, camosine ((J-alanylhistidine) (10—25 mM). The functions of camosine are obscure although it has been suggested to be an effective antioxidant (Pavlov et al., 1993). 

Haydek, J., Parveen, S., List, T., Doria, M. and Keshvarian, A. (1991). Reactive oxygen metabolites in experimental colitis the effect of catalase. Gastroenterology, 100, A585. 

Higuchi, M., Cartier, L.J., Chen, M. and HoUoszy, J.O. (1985). Superoxide dismutase and catalase in skeletal muscle adaptive response to exercise. J. Gerontol. 40, 281-286. Hunter, M.I.S., Brzeski, M.S. and de Vane, P.J. (1981). Superoxide dismutase, glutathione peroxidase and thiobarbi-turic acid-reactive compounds in erythrocytes in Duchenne muscular dystrophy. Clin. Chim. Acta 115, 93-98. 

Kar, N.C. and Pearson, C.M. (1979). Catalase superoxide dismutase, glutathione reductase and thiobarbituric acid-reactive products in normal and dystrophic human muscle. Clin. Chim. Acta 94, 277-280. 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

Normally, the cascade from oxygen to water is well controlled by SOD, catalase and endogenous antioxidants such as glutathione, ascorbate and vitamin E. Vitamin E is the most important membrane-bound antioxidant. However, during ischaemia, the local control of ROS is lost, thus reactive free radicals can attack the membranes and lipid peroxidation begins. Endogenous antioxidants can be supplemented. This section describes this supplementation strategy. 

The effectors of the mammalian host immune attack against filaria include reactive oxygen intermediates. Filarial nematodes express glutathione peroxidase, thioredoxin peroxidase and superoxide dismutase at their surface - enzymes believed to protect the nematode from this attack (Selkirk et al., 1998). A bacterial catalase gene has been identified that most probably derives from the endosymbiont genome (Henkle-Duhrsen et al., 1998) this enzyme may contribute with other enzymes to the protection of both Wolbachia and its nematode host from oxygen radicals. 

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. 

Overproduction of free radicals by erythrocytes and leukocytes and iron overload result in a sharp increase in free radical damage in T1 patients. Thus, Livrea et al. [385] found a twofold increase in the levels of conjugated dienes, MDA, and protein carbonyls with respect to control in serum from 42 (3-thalassemic patients. Simultaneously, there was a decrease in the content of antioxidant vitamins C (44%) and E (42%). It was suggested that the iron-induced liver damage in thalassemia may play a major role in the depletion of antioxidant vitamins. Plasma thiobarbituric acid-reactive substances (TBARS) and conjugated dienes were elevated in (3-thalassemic children compared to controls together with compensatory increase in SOD activity [386]. The development of lipid peroxidation in thalassemic erythrocytes probably depends on a decrease in reduced glutathione level and decreased catalase activity [387]. 

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