Carbon-nitrogen lyases

Succinate dehydrogenase Cytochrome c oxidase Citrate synthase Carbon—nitrogen lyases Forming carbon—nitrogen bonds Acting on carbon-nitrogen bonds, other than peptide bonds Chitinase... 

The ammonia lyases (E. C. 4,3.1.x), which catalyze the addition of amines to carbon-carbon double bonds, belong to the class of carbon-nitrogen lyases. The reactions catalyzed by ammonia lyases are in equilibrium and depending on reaction conditions the reaction can be directed either towards ammonia addition or in the direction of elimination of ammonia. 

Carbon-carbon lyases EC 4.99. Other lyases Carbon-oxygen lyases Carbon-nitrogen lyases Cartxrn-sulfur lyases Carbon-halide lyases... 

EC4 Lyases transfer to or from double EC4.3 Carbon-Nitrogen Lvases (phenylalanine pyruvate pyruvate C02 m-1 -hydroxypyrene- 23... 

A less common reactive species is the Fe peroxo anion expected from two-electron reduction of O2 at a hemoprotein iron atom (Fig. 14, structure A). Protonation of this intermediate would yield the Fe —OOH precursor (Fig. 14, structure B) of the ferryl species. However, it is now clear that the Fe peroxo anion can directly react as a nucleophile with highly electrophilic substrates such as aldehydes. Addition of the peroxo anion to the aldehyde, followed by homolytic scission of the dioxygen bond, is now accepted as the mechanism for the carbon-carbon bond cleavage reactions catalyzed by several cytochrome P450 enzymes, including aromatase, lanosterol 14-demethylase, and sterol 17-lyase (133). A similar nucleophilic addition of the Fe peroxo anion to a carbon-nitrogen double bond has been invoked in the mechanism of the nitric oxide synthases (133). 

Fig. 2. Ball-and-stick representations of two differently oriented asparagine ladders of (A) W-arcade taken from the crystal structures of pectate lyase C (Lietzke et al., 1996) and (b) ppl-arcade taken from l DP-.V-aretylglucosamine acyltransferase (Raetz and Roderick, 1995). b, l, and so on refer to a one-letter conformational code (Fig. IOC). The ladders are viewed from within the respective /(-solenoids. The arrow shows the orientation (N- to C-terminal) of the solenoid. Oxygen atoms are in red, nitrogen in blue, and carbon in green. Dotted lines designate H-bonds of side chains (red) and inter-coil H-bonds of the polypeptide backbone (black). Except for the ladder-forming asparagines, only the backbones of the coils are shown. Panels are reprinted from Hennetin et al. (2006) with the permission of the publisher.

Fig. zi. 1 hree-dimensional structure of the sialate-pyruvate lyase from Escherichia coli. (top) Viewed down the (3-barrel axis from the carboxy-terminal end of this aldolase. The putative catalytic residue Lys-165 is shown in ball-and-stick representation, (bottom) Putative active site of Neu5Ac lyase showing the side chains of nine of the residues forming the surface of the pocket. Carbon atoms are white, oxygens black and nitrogens grey. From ref. [899] by permission of Current Biology Ltd., London. 

Figure 2 Structure of the MIO cofactor in histidine ammonia lyase from Ps. putida. In this enzyme modification of Aia142, Serf 43, and Gly144 yields the MIO cofactor, which is displayed as sticks colored gray for carbon, red for oxygen, and blue for nitrogen. The coordinates from PDB entry 1b8f were used to display this structure.

Figure 3. Model showing possible fates for lipid and carbohydrate carbon during nitrogen assimilation in P. tricomutum. Ruxes shown do not represent actual stoichiometries. (1) glutamine synthetase (2) nitrite reductase (3) nitrate reductase (4) malate glycolysis (5) cytosolic malate dehydrogenase (6) anaplerotic carbon flux (7) gluconeogenesis (8) glycolysis (9) carnitine acyltransferase (10) isocitrate lyase.

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