Tyrosinase cytochrome oxidases

Citrate synthase. Cytochrome c oxidase 3, Tyrosinase, Cytochrome oxidase, DNA polymerase 1... 

Adults require 1-2 mg of copper per day, and eliminate excess copper in bile and feces. Most plasma copper is present in ceruloplasmin. In Wilson s disease, the diminished availability of ceruloplasmin interferes with the function of enzymes that rely on ceruloplasmin as a copper donor (e.g. cytochrome oxidase, tyrosinase and superoxide dismutase). In addition, loss of copper-binding capacity in the serum leads to copper deposition in liver, brain and other organs, resulting in tissue damage. The mechanisms of toxicity are not fully understood, but may involve the formation of hydroxyl radicals via the Fenton reaction, which, in turn initiates a cascade of cellular cytotoxic events, including mitochondrial dysfunction, lipid peroxidation, disruption of calcium ion homeostasis, and cell death. 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

Copper is a component of many enzymes including amine oxidase, lysyl oxidase, ferroxidase, cytochrome oxidase, dopamine P-hydroxylase, superoxide dismutase and tyrosinase. This latter enzyme is present in melanocytes and is important in formation of melanin controlling the colour of skin, hair and eyes. Deficiency of tyrosinase in skin leads to albinism. Cu " ion plays an important role in collagen formation. 

Copper has an essential role in a number of enzymes, notably those involved in the catalysis of electron transfer and in the transport of dioxygen and the catalysis of its reactions. The latter topic is discussed in Section 62.1.12. Hemocyanin, the copper-containing dioxygen carrier, is considered in Section 62.1.12.3.8, while the important role of copper in oxidases is exemplified in cytochrome oxidase, the terminal member of the mitochondrial electron-transfer chain (62.1.12.4), the multicopper blue oxidases such as laccase, ascorbate oxidase and ceruloplasmin (62.1.12.6) and the non-blue oxidases (62.12.7). Copper is also involved in the Cu/Zn-superoxide dismutases (62.1.12.8.1) and a number of hydroxylases, such as tyrosinase (62.1.12.11.2) and dopamine-jS-hydroxylase (62.1.12.11.3). Tyrosinase and hemocyanin have similar binuclear copper centres. 

Cu Cu+, Cu2+ 2 mg Cytochrome c oxidase, tyrosinase, lysyl oxidase, superoxide dismutases Cu deficiency has been associated with atherosclerosis in animals... 

Copper is an essential element to most life forms. In humans it is the third most abundant trace element only iron and zinc are present in higher quantity. Utilization of copper usually involves a protein active site which catalyzes a critical oxidation reaction, e.g., cytochrome oxidase, amine oxidases, superoxide dismutase, ferroxidases, dopamine-/ -hydrox-ylase, and tyrosinase. Accordingly, animals exhibit unique homeostatic mechanisms for the absorption, distribution, utilization, and excretion of copper (J). Moreover, at least two potentially lethal inherited diseases of copper metabolism are known Wilson s Disease and Menkes s Kinky Hair Syndrome (I). 

Copper Hemocyanrn/Tyrosinase Models Copper Proteins with Dinuclear Active Sites Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Cytochrome Oxidase Electron Transfer Reactions Theory Long-range Electron Transfer in Biology Metal Ion Toxicity Metal-related Diseases of Genetic Origin Metallochaperones Metal Ion Homeostasis Nutritional Aspects of Metals Trace Elements. 

The clinical symptoms of classical Menkes disease can be traced back to developmentaUy important copper enzymes such as lysyl oxidase, tyrosinase (see Copper Hemocyanin/Tyrosinase Models), cytochrome c oxidase (see Cytochrome Oxidase), dopamine -hydroxylase, superoxide dismutase, and amine oxidase (see Superoxide Dismutase). Lysyl oxidase is needed for the cross-linking of connective tissue a deficiency in this enzyme causes weakened connective tissue and connective tissue disorder such as arterial ruptures as observed in these patients. Low levels of cytochrome c oxidase cause temperature instability and the absence of tyrosinase explains the hair depigmentation observed in affected individuals. ... 

Copper-dependent enzymes include tyrosinase (which is involved in melanin pigment formation) and the various oxidases (i.e., cytochrome oxidase, superoxide dismutase, amine oxidase, and uricase). Copper plays a major role in the incorporation of iron into the heme of hemoglobin. Copper deficiency is characterized by hypochromic, microcytic anemia resulting from defective hemoglobin synthesis. 

More copper is found in the brain and heart than in any other tissue except for liver, where it is stored as copper thionein and released as ceruloplasmin or in the form of a complex with serum albumin. The high metabolic rate of the heart and brain requires relatively large amounts of copper metalloenzymes including tyrosinase, cytochrome c oxidase, dopamine-/3-hydroxylase, pyridoxal-requiring monamine oxidases, and Cu-Zn superoxide dismutase. Copper deficiency, which can occur for reasons analogous to those discussed above for Fe and Zn, leads to brain disease in infants, anemia (since cytochrome oxidase is required for blood formation), and heart disease. Few details are known about the molecular basis for copper uptake from foods. 

As like the other carbamate herbicides, sulfallate is a mitosis poison. Of the biochemical processes of plants inhibition of protein and RNA synthesis has been demonstrated experimentally (Moreland et al., 1969). It seems certain that sulfallate forms a chelate with tyrosinase and cytochrome oxidase (Anonym, 1974). 

Copper is an essential trace metal which is a component of a wide range of intracellular metalloen/ymes. including cytochrome oxidase, superoxide dismutase. tyrosinase, dopamine hydroxylase and lysyl oxidase. Most of the copper in plasma is associated w-ith the specific copper-binding protein, caeruloplasmin. 

II by AAO III Cytochrome oxidase-cytochrome system IV tyrosinase, laccase or peroxidase system with phenols as donors. Their results have shown that while the Cu (II) and AAO mediated oxidation of AA were almost similarly affected by flavonoid pigments, the oxidation of AA was being inhibited by flavonoids to varying degrees, but those coupled to tyrosinase, laccase and peroxidase were generally stimulated. The same flavonoid may bring about opposite effect depending... 

The amount of copper in the body is 80-100 mg. Copper is a component of a number of oxido-reductase enzymes (cytochrome oxidase, superoxide dismutase, tyrosinase, uricase, amine oxidase). In blood plasma, it is bound to ceruloplasmin, which catalyzes the oxidation of Fe + to Fe +. This reaction is of great significance since it is only the Fe + form in blood which is transported by the transferrin protein to the iron pool in the liver. The daily copper requirement is 1-1.5 mg and it is supplied in a normal diet. Copper is even less desirable than iron during food processing and storage since it catalyzes many unwanted reactions. Cu +-Ions are taste bearing. The threshold value 2.4-3.8 mg/1 was determined with aqueous solutions of CuSOa or CuCl2. 

Copper is an essential trace element for humans and other animals. Copper ions are included in the active centres of many enzymes, especially cytochrome c oxidase, superoxide dismutase, various aminoxidases (such as lysyl oxidase), hydroxylases (e.g. dopamine -hydroxylase and tyrosinase), galactose oxidase or different phenoloxidases, such as laccase and other oxidoreductases. The so-called blue copper proteins, for example plastocyanin, azurin and plantacyanin, occur in many prokaryotic organisms and plants. These proteins, by a change to the bound copper valency, provide electron transfer in various redox processes. 

The evidence at present available suggests that the formation of no copper-protein other than caeruloplasmin is disturbed in Wilson s disease. An abnormality of cytochrome oxidase itself would surely be incompatible with life, tyrosinase also does not appear to be abnormal since widespread disturbances of pigmentation are rare indeed [73]. I have seen abnormal skin pigmentation only once in over 70 cases, this was clearly melanin deposited at the site of purpuric haemorrhages on the dorsum of the feet and ankles. Neither have there been any reports of abnormal pigmentary deposits in the brain. The copper content of hair and nails is also normal [74, 75, 76]. 

Another problem to be elucidated is the role of copper in cytochrome a. In the known copper enzymes such as tyrosinase and laccase, copper is an important component of the prosthetic group, but is released from the protein moiety by dialysis against potassium cyanide. In the case of cytochrome a, however, the mode of combination of copper must be different, since very little copper is released from the protein moiety by dialysis. The best known method of releasing the copper is by acid treatment. The role of copper in the electron trasnferring system is still obscure, though Cohen and Elvehjem (1934), Yoshikawa (1937), Schultze (1939, 1941), Gallagher et al. (1956), and Gubler et al. (1957) observed, from dietary experiments, that copper-deficient tissues and yeast have a low cytochrome oxidase activity and a decreased content of hemin a. 

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

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