Hydroxylase/desaturase

Broun P, Boddupalli S, Somerville C. (1998) A bifunctional oleate 12-hydroxylase desaturase from Lesquerella fendleri. Plant 713 201-210. 

Figure 73. The carotenoid biosynthetic pathway. Enzymes are named according to the designation of their genes Ccs, capsanthin-capsorubin synthase CrtL-b, lycopene-b-cyclase CrtL-e, lycopene-e-cyclase CrtR-b, b-ring hydroxylase, CrtR-e, e-ring hydroxylase DMADP, dimethylallyl diphosphate GGDP, geranylgeranyl diphosphate Ggps, geranylgeranyl-diphosphate synthase IDP, isopentenyl diphosphate Ipi, IDP isomerase Pds, phytoene desaturase Psy, phytoene synthase Vde, violaxanthin de-epoxidase Zds, z-carotene desaturase Zep, zeaxanthin epoxidase. (From van den Berg and others 2000.)...

Figure 13.25 Three-dimensional structures of diiron proteins. The iron-binding subunits of (a) haemery-thrin, (b) bacterioferritin, (c) rubryerythrin (the FeS centre is on the top), (d) ribonucleotide reductase R2 subunit, (e) stearoyl-acyl carrier protein A9 desaturase, (f) methane monooxygenase hydroxylase a-subunit. (From Nordlund and Eklund, 1995. Copyright 1995, with permission from Elsevier.)...

ACYL-CoA DESATURASE ALKANE HYDROXYLASE AMINE OXIDASES... 

The origin of ricinoleic acid, an abundant constitu-tuent of castor beans, is also shown in Fig. 21-2. It is formed by an oleate hydroxylase that has an amino acid sequence similar to those of oleate desaturases.113 Both hydroxylation and desaturation are reactions catalyzed by diiron centers.114 Other fatty acid hydroxylases act on the alpha115 and the omega positions. The latter are members of the cytochrome P450 family.116 117... 

Shanklin J., Whittle E. and Fox B. G. (1994) Eight histidine residues are catalytically essential in a membrane associated iron enzyme, stearoyl-CoA desaturase and are conserved in alkane hydroxylase and xylene monooxygenase. Biochem. 33, 12787-12794. 

Triricinolein (RRR) constitutes about 70% of TAG in castor oil (Lin et al., 2003). Recently, a new tetraacylglycerol, (12-ricinoleoylricinoleoyl)diricinoleo ylglycerol (RRRR), in castor oil was identified and its content was about 0.5% (Lin et al., 2006). These two AG contain ricinoleate only without other FA. The biosynthetic pathway of RRR and RRRR in the castor bean has been established and the key enzymatic steps driving ricinoleate into RRR and RRRR have been identified (Lin et al., 1998, 2000, 2002, 2006) as shown in Figure 25.1. Oleate of oleoyl-CoA is incorporated into 2-oleoyl-phosphatidylcholine (2-oleoyl-PC) by lysophosphatidylcholine-acyltransfer-ase and then hydroxylated to 2-ricinoleoyl-PC by 12-oleoyl-hydroxylase in castor microsomes (Fig. 25.1) (Lin et al., 1998). 2-Oleoyl-PC is also desaturated to 2-linoleoyl-PC and then to 2-linolenoyl-PC (Lin et al, 1998) by desaturases. 

Figure 4 Variations on an oxidative theme the dehydrogenation/oxygenation connection. C-12-initiated oxidation catalyzed by oleate desaturase and its homolog oleate 12-hydroxylase (a) and acetylenase and its homolog epoxidase (b).

Howling D, Morris LJ, Gurr MI, James AT. The specificity of fatty acid desaturases and hydroxylases the dehydrogenation and hydroxylation of monoenoic acids. Biochim. Biophys. Acta... 

The presentation in 1993 of the structure of the hydroxylase component of methane monooxygenase (MMOH) by Rosenzweig et al. (15) is the third published three-dimensional structure of a diiron-oxygen protein (Fig. 1). The previous two are from hemerythrin (Hr) (16,17) and protein R2 of E. coli ribonucleotide reductase (RNR-R2) (18, 19). Some other dinuclear iron proteins with known fi-oxo or p.-hydroxo bridges are purple acid phosphatases (PAP) [(e.g., uteroferrin (Uf)] (20, 21), ferritins (in early stages of nucleation) (22), rubrerythrin (Rr) (23-26), nigerythrin (26), and soluble stearoyl-acyl carrier protein A desaturase (A-AGP) (27, 28). 

Fig. 11.3 Simplified diagram of isoprenoid metabolic pathway relative to the conversions among carotenoids that have been genetically manipulated. Enzymes catalysing some key reactions are indicated by the following abbreviations IPI, isopentenyl pyrophosphate isomerase PSY, phytoene synthase PDS, phytoene desaturase (crti, gene from Erwinia uredovora) ZDS, -carotene desaturase LCYB, lycopene / -cyclase CRTR-b, /3-carotene 3,3 -hydroxylase CCS, capsanthin-capsombin synthase CRTO, /3-carotene ketolase.

Mochizuki, H., K. Suhara, and M. Katagiri (1992). Steroid 6p-hydroxylase and 6-desaturase reactions catalyzed by adrenocortical mitochondrial P-450. J. Steroid Biochem. Mol. Biol. 42, 95-101. 

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