Dioxygenase heme-containing

As can be seen in this figure, although the conversion of the nitrogen compounds is observed, nitrogen still remained in the products formed. l-Tryptophan 2,3-dioxygenase (Scheme 19a) from several bacterial strains is a heme-containing enzyme. 

Cobaltn-Schiff base complexes, e.g. Co(salen),567 Co(acacen)568 and cobalt(II) porphyrins,569 e.g. Co(TPP), are effective catalysts for the selective oxygenation of 3-substituted indoles to keto amides (equation 249), a reaction which can be considered as a model for the heme-containing enzyme tryptophan-2,3-dioxygenase (equation 21).66 This reaction has been shown to proceed via a ternary complex, Co-02-indole, with probable structure (175), which is converted into indolenyl hydroperoxide (176). Decomposition of (176) to the keto amide (174) readily occurs in the presence of Co(TPP), presumably via formation of a dioxetane intermediate (177).569,56 Catalytic oxygenolysis of flavonols readily occurs in the presence of Co(salen) and involves a loss of one mole of CO (equation 251).570... 

The metal-containing dioxygenases usually contain iron, either as a heme group or, more usually, as non-heme iron. 

II. CATALYSIS OF 02 TRANSFER INTO SUBSTRATES BY HEME-CONTAINING DIOXYGENASES... 

Actually, it is noteworthy that there are examples of heme-containing dioxygenases that bind 02 with formation of a heme—Fe(II)—02 complex. This is the case of indolamine-2,3-dioxygenase (EC 1.13.11.11) and tryptophan-2,3-dioxygenase, which catalyze the insertion of 02 into L-tryptophan to yield A-for-mylkynurenine [21], The catalytic cycle involves the ternary complex L-trypto-phan-iron(II) enzyme-02 as an active intermediate. In this ternary complex, which yields A-formylkynurenine and the Fe(II) enzyme, 02 and/or the substrate is activated [21], a situation clearly different from that found for PGHS. 

In contrast to eukaryotes, bacteria such as Pseudomonas putida employ non-heme-containing dioxygenases in benzene metabolism [6-14. Harpel and Lipscomb [42] postulated that intradiol dioxygenases chelate the substrate (see 35) and the ring-opened product (see 36) releasing (Z,Z)-muconic acid (4a) (see Scheme... 

There is another class of enzymes which may resemble mechanistically the extradiol dioxygenases. None of their substrates however can form quinones. They also show diversity in their co-factors and include cupro-and ferro-proteins as well as two heme-containing enzymes. 

Examples include the liver enzymes, homogentisate dioxygenase (oxidase) and 3-hydroxyantliranilate dioxygenase (oxidase), that contain iron and L-trypto-phan dioxygenase (tryptophan pyrrolase) (Chapter 30), that utilizes heme. 

A large number of iron-containing proteins form nitrosyl complexes. Heme proteins, iron-sulfur proteins, and other iron proteins such as nonheme iron dioxygenases all form characteristic nitrosyl complexes. In enzymes in which the metal center has an open coordination position, NO often can be bound without severe disruption of the site. This introduces the possibility of reversibility of inhibition. 

Cytochrome c oxidase contains one heme a and one heme a, besides two copper atoms Cu EPR detectable when oxidized and CUj EPR undetectable With L-tryptophan 2,3-dioxygenase (EC 1.13.11.11), another heme protein, it has been... 

Brady, F. O., Udom, A. Is indoleamine 2,3-dioxygenase another heme and copper containing enzyme In Iron and Copper Proteins. Adv. Experim. Med. Biol., Vol. 74 (Yasunobu, K. T., Mower, H. F., Hayaishi, O., eds.). New York-London Plenum, 1976, pp. 343-353... 

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