Phenoxazinone synthase

Normal copper enzymes Phenoxazinone synthase Superoxide dismutase... 

Other Copper Oxidases. A number of additional multicopper oxidases have been detected [22], including phenoxazinone synthase (Table 1). This enzyme catalyzes the overall six-electron oxidative coupling of 2-aminophenols to form 1-aminophenoxazinone, the final step in the bacterial (Streptomyces) biosynthesis of the antineoplastic agent actinomycin. 

As expected, the ascorbate oxidases are very closely related to each other. The bacterial proteins phenoxazinone synthase and the copper resistance gene product from P. syringae are very distant from the other proteins included in Table V. The rape BplO gene product exhibits significant similarity to ascorbate oxidase (about 72% differences). 

Jones, G. and D.A. Hopwood (1984). Molecular cloning and expression of the phenoxazinone synthase gene from Streptomyces antibioticus. J. Biol. Chem. 259 2703-2714. 

Purification has been reported of phenoxazinone synthase, the enzyme which catalyses phenoxazinone formation from 4-methyl-3-hydroxyanthranilic acid (123) in the biosynthesis of actinomycin (124). Two forms of the enzyme, one of high and one of low molecular weight, were isolated. The relative amount of the... 

Laccase, ascorbate oxidase, and ceruloplasmin are the classical members of the multicopper oxidase family also known as blue oxidases. Recently, a small number of bacterial members of this family have been characterized, including CueO from E. coli a spore-coat laccase (CotA) from Bacillus suhtilis and phenoxazinone synthase from Streptomyces antibioticus The catalyzed reaction of these enzymes except for phenoxazinone synthase is given in Equation (11). A comprehensive overview of the broad and active research on blue copper oxidases is presented in Messerschmidt. Recent results have been included in a review on the reduction of dioxygen by copper-containing enzymes. The nature and number of the different copper sites in blue oxidases has been described in the sections about the type-1 copper site and the trinuclear copper cluster. 

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... 

The final reaction, leading to the active molecule, is catalysed by another enzyme, phenoxazinone synthase. This enzyme has been isolated from Str. antibioticus [55] and can exist in a dimeric form, with lower activity, and in a hexameric form, with higher activity, depending on the age of the cultures [185]. The enzyme, cloned in Str. lividans [186] contains 4-5 copper ions. However, only 3 copper ions are functionally active, and can accept electrons from substrates [187]. 

Phenoxazinone synthase (PHS) was first identified in extracts of S. antibioticus by Katz and Weissbach (15). The enzyme was shown to catalyze the oxidative condensation of two molecules of 2-aminophenol and its derivatives to yield the relevant phenoxazinone (Figure 3). Thus, the enzyme can catalyze the condensation of 3-HA or 4-MHA to yield cinnabarinic acid or actinocin, respectively, and will also function with 3-HA or 4-MHA peptides to yield actinocinyl peptides (26). At one time, it was thought that the actinocinyl peptides were intermediates in the acm biosynthetic pathway, but the work of Keller and coworkers, described in this chapter, argues strongly for the condensation of 4-MHA pemapeptides as the ultimate or penultimate step in the process. 

Phenoxazinone synthase was purified to homogeneity by Choy and Jones (27). These workers confirmed the oxygen requirement for PHS activity (Figure 3) and also demonstrated that the enzyme exists in two forms in S. aniibiotrcws. A large form, L,... 

Figure 6 Assembly of 4-MHA and the five constituent amino acids in the synthesis of 4-MH.A pentapeptide lactone D. The conesponding actinomycin D arises by oxidative condensation of two of these 4-MHA pentapeptide lactone moieties, catalyzed by phenoxazinone synthase. Sar = sarcosine (N-methylglycine) MeVal M-methyl-L-valine.

Choy HA, Jones GH, Phenoxazinone synthase from Srreptomyces antibioticus Purification of the large and small enzyme forms. Arch Biochem Biophys 1981 211 55-65. 

Barry CE III. Pannesh G, Nayar PG, Begley T. Phenoxazinone synthase Mechanism for the formation of the phenoxazinone chromophore of actinomycin. Biochem 1989 ... 

Freeman JC, Nayar PG, Begley TP, Villafranca JJ. Stoichiometry and spectroscopic identity of copper centers in phenoxazinone synthase A new addition to the blue copper oxidase... 

Hsieh C J, Jones GH. Nucleotide sequence, transcriptional analysis and glucose regulation of the phenoxazinone synthase gene (phsA) from Streptomyces antibiotic . J Bacreriol 1995 177 5740-5747. 

Marshall R, Redfield B, Katz E, Weissbach. H. Changes in phenoxazinone synthase activity during the growth cycle of Sirepcomyces antibiottciis. Arch Biochem Biophys 1968 123J17-323. 

Jc ies GH. Regulation of phenoxazinone synthase expression in Streptomyces ontibioociis. J Bacteriol 1985 163 1215-1221. 

Jones GH, Hopwood DA. Activation of phenoxazinone synthase expression in Sirepiomyces lividam by cloned DNA sequences from Streptomyces (mtibioticus. J Biol Chem 1984 259 14158-14164. 

Madu AC, Jones GH. Molecular cloning and in vitro expression of a silent phenoxazinone synthase gene from Streptomyces lividans. Gene 1989 84 287-294. 

X-ray structure(s) available Number of active site of Gu ions with multiple entries indicating more than one type of site. Uncoupled dioopper center FET3, phenoxazinone synthase, bilirubin oxidase, dihydrogeodin oxidase, and sulochrin oxidase also belong to this class. 

In most cases the mechanism by which nutrients control secondary metabolism is unknown. However, glucose and other rapidly used carbon sources repress the formation of iV-acetylkanamycin amidohydrolase, thought to be the final enzyme of kanamycin A biosynthesis (D 1.3) and phenoxazinone synthase, an enzyme required in actinomycin biosynthesis (D 8.4.1). 

Galactose oxidase Glyoxal oxidase Phenoxazinone synthase... 

This system can be regarded as a functional model of Phenoxazinone synthase, which is involved in the biosynthesis of Actinomycin D (AD), a... 

Ascorbate oxidase Phenoxazinone synthase Galactose oxidase Amine oxidase... 

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