Oxidase Activity

Mechanism of the Oxidase Activity. Considerable work has been done toward elucidating the mechanism of action of ceruloplasmin s oxidase activity. 

There have been basically two approaches to the problem the use of classical steady state kinetic analyses and the application of the various methodologies applicable to the brief transient phase as the enzyme-substrate mixture approaches the steady state or independently interacts with either a reductant or oxygen. 

Two major experimental difficulties cloud the interpretation of the kinetic results. The first and least important of these is the effect of intermediary free radicals as substrates of the enzyme, and the second and most important is the role of iron salts in both the steady state kinetics of ceruloplasmin mediated oxidations of various substrates and on the rates of the individual reactions between substrates and enzyme. The latter is in contrast to Rhus laccase whose kinetic behavior is uninfluenced by free iron 97). 

Two of the most commonly used substrates of ceruloplasmin are paraphenylene-diamine (PPD) and N, N-dimethyl-paraphenylenediamine (DPD). DPD, which has been used most extensively, is oxidized in a one-electron process to DPD+ which is intensely colored and allows ready observation of the course of the reaction. It has been well established that both substrates are initially oxidized to their respective radical cations. Broman et al. (88) studied the oxidation of PPD, observed free radical formation during catalysis, and identified this species as PPD+ by EPR techniques. Very convincing evidence was also presented that this free radical was neither bound to the enzyme nor acted as a substrate toward ceruloplasmin, but instead rapidly disproportionated to PPD and the quinoid form of PPD. 

The same reaction scheme does not hold for DPD where the cation radical, DPD+, also serves as a substrate for ceruloplasmin. 

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Vanadium. Vanadium is essential in rats and chicks (85,156). Estimated human intake is less than 4 mg/d. In animals, deficiency results in impaired growth, reproduction, and Hpid metaboHsm (157), and altered thyroid peroxidase activities (112). The levels of coen2yme A and coen2yme Q q in rats are reduced and monoamine oxidase activity is increased when rats are given excess vanadium (157). Vanadium may play a role in the regulation of (NaK)—ATPase, phosphoryl transferases, adenylate cyclase, and protein kinases (112). 

FIGURE 25.42 The mixed-function oxidase activity of 7ff-hydroxylase. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

For example, a screening of 416 strains (71 bacterial strains, 45 actinomycetes, 59 yeast, 60 basidiomycetes, 33 marine fungi, and 148 filamentous fungi) has been performed to look for microorganisms that display reductase activity in the absence of oxidase activity [8b]. A new microorganism, Diplogdasinospora grovesii IMI... 

Cosio C. Vuillemin L. De Meyer M. Kevers C. Penel C. Dunand C. (2009) An anionic class III peroxidases from zuccini may regulate hypocotyl elongation through its auxin oxidase activity / / Planta. V. 229. P. 823-836. 

Zakharova and co-workers studied a red variety in 1997 to gain a closer insight into its polyphenol oxidase activity. More recently, a study addressing the antioxidant properties of a red colored Swiss chard was published. However, the pigments were erroneously addressed as anthocyanins. 

Hewitt LM, JH Carey, KR Munkittrick, JL Parrott, KR Solomon, MR Servos (1998) Identification of chloro-nitro-trifluoromethyl-substituted dibenzo-/ -dioxins in lampricide formulations of 3-trifluoromethyl-4-nitrophenol assessment to induce mixed function oxidase activity. Environ Toxicol Chem 17 941-950. 

Chakrabarti SK, Loua KM, Bai C, Durham H, Panisset JC. 1998. Modulation of monoamine oxidase activity in different brain regions and platelets following exposure of rats to methyhnercury. Neurotoxicol Teratol 20 161-168. 

Marker, H.S., Weiss, C., Silides, D.J., and Cohen, G. (1981). Coupling of dopamine oxidation (monoamine oxidase activity) to glutathione oxidation via the generation of hydrogen peroxide in rat brain homogenates. J. Neurochem. 36, 589-593. 

Reperfusion of the synovial membrane occurs when exercise is stopped and O2 is subsequently reintroduced to the tissue. O2 is a substrate required for xanthine oxidase activity and O2" is generated. Therefore, repeated cycles of rest-exercise-rest in the inflamed joint may provide a continuous flux of destructive ROM. 

Blake, D.R., Blann( A., Bacon, P.A., Farr, M., Gutteridge, J.M.C. and Halliwell, B. (1983). Ferroxidase and ascorbate oxidase activities in synovial fluid from rheumatoid joints. Clin. Sci. 64, 551-553. 

Pence, B.C. and Reiners, J.J. (1987). Murine epidermal xanthine oxidase activity correlation with degree of hyperplasia induced by tumor promoters. Cancer Res. 47, 6388-6392. 

This correlated with a 64% decrease in endogenous hepatic xanthine dehydrogenase/oxidase activity. 

Phon, S.H., Gannon, D.E., Varan, J., Ryan, V.S. and Ward, P.A. (1989). Xanthine oxidase activity in rat pulmonary artery endothelial cells and its alteration by activated neutrophils. Am. J. Path. 134, 1201-1211. 

Pitt, R.M., McKelvey, T.G., Saenger, J.S., Shah, A.K., Jones, H.P., Manci, E.A. and Powell, R.W. (1991). A tungsten-supplemented diet delivered by transplacental and breastfeeding routes lowers intestinal xanthine oxidase activity and affords cytoprotection in ischaemia-reperfusion injury to the small intestine. J. Paediatr. Suig. 26, 930-935. 

Cytochrome c oxidase activity in lung mitochondria of Fisher-344 rats was significantly decreased at 50 ppm (15%), 200 ppm (43%), and 400 ppm (68%) hydrogen sulfide compared to controls after a 4-hour exposure (Khan et al. 1990). Cytochrome c oxidase activity had returned to normal for animals exposed to 200 ppm, but not for those exposed to 400 ppm, by 24 hours postexposure. Succinate oxidase activity was reduced at 200 ppm (40%) and 400 ppm (63%) but was not affected at 50 ppm (Khan et al. 1990). 

NS (acute) (general population) Hepatic Decreased mixed function oxidase activity NS (children) Alvares et al. 1975 Saenger et al. 1984... 

Hamase, K., Inoue, T., Morikawa, A., Konno, R., Zaitsu, K. (2001). Determination of free d-proline and D-leucine in the brains of mutant mice lacking D-amino acid oxidase activity. Anal. Biochem. 298, 253-258. 

Fetterer, R.H. and Hill, D.E. (1993) The occurrence of phenol oxidase activity in female Trichuris suis. Journal of Parasitology 79, 155—159. 

The parasitic nematode, Ascaris suum, undergoes a number of well-characterized metabolic transitions during its development (Table 14.1), but little is known about the regulation of these events (Barrett, 1976 Komuniecki and Komuniecki, 1995). Adults reside in the porcine small intestine and fertilization takes place under low oxygen tensions. The unembryonated egg that leaves the host is metabolically quiescent, has no detectable cytochrome oxidase activity or ubiquinone and appears to be transcriptionally inactive (Cleavinger et al., 1989 Takamiya et al., 1993). Embryonation requires oxygen and after about 48-72 h is accompanied by... 

Oya, H., Costello, L.C. and Smith, W.N. (1963) The comparative biochemistry of developing Ascaris eggs. II. Changes in cytochrome c oxidase activity during embryonation. Journal for Cellular and Comparative Physiology 62, 287—294. 

Dioxygen reduction (oxidase activity) and activation for incorporation into organic substrates are catalysed by a number of mononuclear non-haem iron enzymes. We will first consider the intramolecular dioxygenases, in which both atoms of oxygen are introduced into the substrate, then the monoxygenases (in which we choose to include the pterin-dependent hydroxylases), the large family of a-hetoacid-dependent enzymes, and finally isopenicillin N-synthase. 

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