Copper-Containing Oxidases

Aromatization can also be accomplished by oxidative cascade reactions-a strategy often utilized by natural product biosynthesis [33]. For example, the phenoxazinone chromophore of actinomycin was proposed to be generated by a six-electron oxidation of aminophenols catalyzed by a copper-containing oxidase (Scheme 7.8) [34]. 

Reinhammer, B. The copper-containing oxidases. In Adv. Inorg. Biochemistry. Vol. 1 (Eichhom, G. L., Marzilli, L. G., eds.). New York-Amsterdam-Oxford Elscvier/North-HoUand, 1979, pp, 91-118... 

Crosslinking of collagen is initiated by oxidation of some of the lysyl and hydroxylysyl side chains from amino groups to aldehyde groups under the action of a copper-containing oxidase (Eq. 8-8, Chapter 18). The aldehyde groups enter into a variety of reactions that... 

Tire most studied of all copper-containing oxidases is cytochrome c oxidase of mitochondria. This multisubunit membrane-embedded enzyme accepts four electrons from cytochrome c and uses them to reduce 02 to 2 H20. It is also a proton pump. Its structure and functions are considered in Chapter 18. However, it is appropriate to mention here that the essential catalytic centers consist of two molecules of heme a (a and a3) and three Cu+ ions. In the fully oxidized enzyme two metal centers, one Cu2+ (of the two-copper center CuA) and one Fe3+ (heme a), can be detected by EPR spectroscopy. The other Cu2+ (CuB) and heme a3 exist as an EPR-silent exchange-coupled pair just as do the two copper ions of hemocyanin and of other type 3 binuclear copper centers. 

The phenomenon of bioelectrical catalysis with direct electron transfer from electrode to enzyme active site was primarily observed in the study of electrochemical oxygen reduction in the presence of a copper-containing oxidase - laccase, adsorbed on electrodes of different origins. This work was developed with peroxidase and hydrogenase application as the working components [2],... 

For certain blue single-copper proteins it was proposed long ago that a Cu(II) or Cu (II)-related band is present between 300-350 nm (28), but it has attracted only very limited attention in spite of the potential implications for the study of blue copper-containing oxidases. A sum-... 

Reinhammar, B., Malmstrom, B. G. Blue copper-containing oxidases, in Copper Proteins (ed.) Spiro, T. G., chapter 3, New York, Wiley-Intersdence 1981... 

Tyrosinase is a copper-containing oxidase (Coche-Guerente et al, 2001 Forzani et al, 2000), which possesses the two different activities illustrated in Figure 57.12. In the first step, referred to as the hydroxylase or cresolase activity, molecular oxygen is used to hydroxylate phenol to form catechol. In the second step, known as the catecholase activity, the enzyme oxidizes catechol to o-quinone, which is simultaneously oxidized by oxygen to its original form, with the production of water. The o-quinone is electro-chemically active and can be reduced back to catechol, as illustrated above in Eq. (57.17). 

It was the aim of this chapter to demonstrate the progress in the field of the blue-copper-containing oxidases during the last 10 years. 

The first two steps in the synthesis of melanin are catalyzed by tyrosinase, a copper-containing oxidase, which converts tyrosine to dopaquinone. All subsequent reactions presumably occur through nonenzymatic auto-oxidation, in the presence of zinc, with formation of the black to brown pigment eumelanin. The yellow to reddish brown, high-molecular-weight polymer known as pheomelanin and the low-molecular-weight trichromes result from addition of cysteine to dopaquinone and further modification of the products. Pheome-lanins and trichromes are primarily present in hair and feathers. 

BG Mahnstrom, L-E Andreasson, B Reinhammar. Copper-containing oxidases and superoxide dismutase. In The Enzymes, Vol.l2. PD Boyer, ed. New York Academic Press, 1975, pp. 507-579. 

Nitrosomas europaea cytochrome c oxidase purified from the bacterial cells cultured in a copper-deficient medium has 1 copper atom per 2 molecules of heme A. As the copper-deficient oxidase does not show g = 2.0 signal in EPR spectrum, it seems not to have Cua. However, the copper-deficient oxidase catalyze the oxidation of horse ferrocytochrome c at the same rate as the two- (or three)-copper containing oxidase does, though its activity to catalyze the oxidation of N. europaea ferrocytochrome c-552 is one third of that of the two- (or three)-copper oxidase (Numata et al., 1989). These results suggest that cytochrome c oxidase needs not necessarily Cua to catalyze the oxidation of ferrocytochrome c. Thus, from Rhodobacter sphaeroides, cytochrome cbb3 has been obtained, which does not have Cua and still shows cytochrome c oxidase activity (Garcia-Horsman et al., 1994). 

The lag time effect probably results from the inhibition of copper-containing oxidases and other copper-catalyzed oxidative processes in apple by Sporix. These oxidative reactions normally would bring about the rapid loss of AA and permit browning to occur once the added AA was depleted (18). Sporix also would inhibit PPO directly by chelation of its copper (3), thereby decreasing the rate of polyphenol oxidation and subsequent browning. The ability of Sporix to exert its effect on enzymatic browning by these two independent mechanisms probably accounts for the apparent synergism obtained with Sporix-AA combinations. 

In a search for a possible biochemical means of investigating the mode of action of LSD it was noted that the administration of this drug to animals resulted in an elevation of brain 5-HT levels and a depression of brain catecholamine levels (Barchas and Freedman, 1963 Koenig-Bersin et al., 1970). It therefore seemed of interest to study the effects of LSD on an enzyme which could utilize both NA and 5-HT as substrates since it was considered that such an enzyme could be used as a model for those central receptors with which LSD must interact in order to produce its characteristic central effects. The enzyme which was eventually selected for study in this way was the copper-containing oxidase caeruloplasmin which utilizes both NA and... 

The copper-containing oxidase caeruloplasmin was studied as a potential model for those receptors in the CNS with which certain centrally acting drugs must interact in order to produce their characteristic effects. 

Type-2, or normal, Cu has undetectable absorption and the EPR line shape of the low-molecular-mass copper complexes (A >0.014Ocm ). Type-2 copper centers are present in copper-containing oxidases... 

The blue oxidases-related enzymes include phenoxazinone synthase from S. antibioticus This enzyme is a copper-containing oxidase that catalyzes the coupling of 2-aminophenols to form the 2-aminophenoxazinone chromophore. This reaction constitutes the final step in the biosynthesis of the potent antineoplastic agent actinomycin. The crystal structure of the oxidized form phenoxazinone synthase from S. anibioticus has been determined. It has been solved in his hexameric form. One monomer is very similar to Iaccase or ascorbate oxidase but it contains a long loop, which connects two domains and stabilizes the hexameric structure. Bound... 

B. Reinhammar B. G. Malmstrom, Blue Copper-Containing Oxidases. In Copper Proteins, Metai Ions in Bioiogy] T. G. Spiro, Ed. John Wiley Sons New York, 1981 Vol. 3, pp 109-149. 

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