Fatty acyl hydroxylase

Broun, P., and Somerville, C. 1997. Accumulation of ricinoleic, lesquerolic, and deni-polic acids in seeds of transgenic Arabidopsis plant that express a fatty acyl hydroxylase cDNA from castor bean. Plant Physiol., 113, 933-942. 

S Fatty acyl hydroxylase. Hydroxylation of oleic acid to ricinoleic acid is a singularly significant reaction occurring in castor bean endosperm (Stumpf, 1989 Vignolo and Naughton, 1991). The enzyme activity of oleate A12-hydroxylase (EC 1.14.13.26) shows particular selectivity for 2-... 

Ng, S., and Jaworski, J.G. (2010) The cytochrome P450 GYP85A22 is a fatty acyl-GoA omega-hydroxylase essential for Estolide synthesis in the stigma of Petunia hybrida. J. Biol Chem., 285, 3985-3996. 

In plants, the cw-hydroxylase system is responsible for synthesis of cw-hydroxy fatty acyl components of cutin and suberin (Section 1.9 and 2.11). The reaction has been studied in preparations from Vida faba with NADPH and oxygen as the required cofactors (Kolattukudy, 1980). The true substrate for o>-hydroxylation of palmitate is the free acid and the active subcellular preparation is the microsomal fraction. The reaction showed the properties of a classic mixed-function oxidase, being inhibited by o-phenanthroline, 8-hydroxyquinoline (metal ion chelators), sodium azide and thiol-directed reagents. The involvement of cytochrome P-450 in the V.faba system is unproven. Although the hydroxylation is inhibited by carbon monoxide, this inhibition was not reversed by light at 420-460 nm. Thus if a cytochrome P-450 is involved in the system it must have unusual properties when compared to other cyto-... 

Covello, P.S. and Reed, D.W. (1996) Functional expression of the extraplastidial Arabidopsis thaliana oleate desaturase gene (FAD2) in Saccharomyces cerivisiae. Plant Physiol. Ill, 223-226. van de Loo, F.N., Broun, P., Turner, S., Somerville, C.R. (1995) An oleate 12- hydroxylase from castor (Ricinus communis L) is a fatty acyl desaturase homologue, Proc. Natl Acad. Sci. USA 92, 6743-6747. 

Figure 1. Electron transport chains of the endoplasmic reticulum. (A) Microsomal acyl-Co A desaturation system composed of NADH-cytochrome reductase, cytochrome fos (a flavoprotein), and fatty acyl-CoA desaturase. (B) Microsomal hydroxylase system depicting participation of the NADPH-cytochrome P-450 reductase (a flavoprotein), cytochrome P-450, and phosphatidylcholine. The role of the phospholipid appears to be in enhancing interaction of the proteins. The reduced form of the hemoprotein cytochrome P-450, on addition of carbon monoxide, envinces a Soret maximum at 450 nm, accounting for its designation. There is evidence that these two systems (A and B) interact in the membrane.

The branched-chain fatty acid, phytanic acid, is not a substrate for acyl CoA dehydrogenase due to the methyl group on its third (P) carbon (Figure 16.22). Instead, it is hydroxylated at the a-carbon by fatty acid a-hydroxylase. The product is decarboxylated and then activated to its CoA derivative, which is a substrate for the enzymes of P-oxidation. [Note Refsum disease is a rare, autosomal recessive disorder caused by a deficiency of a-hydroxylase. This results in the accumulation of phytanic acid in the plasma and tissues. The symptoms are primarily neurologic, and the treatment involves dietary restriction to halt disease progression.]... 

Ferrous ion-induced Hpid peroxidation of rat liver mitochondria was accelerated by phosphate (Yamamoto et al. 1974). Preincubation of rat liver microsomes with iron (Fe)/ascorbate (50 pM/ 200 pM), known to induce peroxidation, resulted in a significant inhibition of (i) the rate-limiting enzyme in cholesterol biosynthesis, HMG-CoA reductase (46 %, P <0.01, (ii) the crucial enzyme control-Hng the conversion of cholesterol in bile acids, cholesterol 7a-hydroxylase (48%, P <0.001), and (iii) the central enzyme for cholesterol esterification, acyl-CoAxholesterol acyltransferase (ACAT, 80%, P <0.0001) (Brunet etal. 2000). The disturbances of these key enzymes coincided with a high rate of malondialdehyde production (350%, P <0.007) and the loss of polyunsaturated fatty adds (36.19 1.06% vs. 44.24 0.41% in controls, P <0.0008). While a-tocopherol simultaneously neutrahsed lipid peroxidation, preserved microsomal fatty acid status, and restored ACAT activity, it was not effective in preventing Fe/ascorbate-induced inactivation of both HMG-CoA reductase (44%, P <0.01) and cholesterol 7a-hydroxylase (71%, P< 0.0001). 

Methods w ere determined for the preparation of cell extracts and membranes. Assays w ere set up for o>-oxidation enzymes (cytochrome P-450 hydroxylase, cviochrome P-450 reductase, alcohol oxidase, aldehyde dehydrogenase) and p-oxidation enz>mes (acyl CoA oxidase, hydratase). Conditions were established for cell growth, and induction of fatty acid oxidising enzymes, under laboratory conditions using C. cloacae parent and mutant strains. 

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