Publications

• Arabidopsis mutants deficient in polyunsaturated fatty acid synthesis. Biochemical and genetic characterization of a plant oleoyl-phosphatidylcholine desaturase.

  Miquel M., Browse J.

  The overall fatty acid composition of leaf lipids in a mutant of Arabidopsis thaliana was characterized by reduced levels of polyunsaturated 18-carbon fatty acids and an increased proportion of oleate as a consequence of a single recessive nuclear mutation. Quantitative analysis of the fatty acid ... >> More

  The overall fatty acid composition of leaf lipids in a mutant of Arabidopsis thaliana was characterized by reduced levels of polyunsaturated 18-carbon fatty acids and an increased proportion of oleate as a consequence of a single recessive nuclear mutation. Quantitative analysis of the fatty acid composition of individual lipids demonstrated that all the major phospholipids of the extrachloroplast membranes are affected by the mutation, whereas the chlorplast lipids show fatty acid compositions only slightly different from those of wild type plants. These results are consistent with the parallel operation of two pathways of lipid synthesis in plant leaf cells (the prokaryotic pathway in the chloroplast and the eukaryotic pathway in the endoplasmic reticulum) and with genetic evidence (Browse, J., Kunst, L., Anderson, S., Hugly, S., and Somerville, C.R. (1989) Plant Physiol 90, 522-529) that an independent 18:1/16:1 desaturase operates on chloroplast membrane lipids. Direct enzyme assays confirmed that the mutant plants are deficient in the activity of a microsomal oleoyl-phosphatidycholine desaturase and demonstrated that this desaturase is the major enzyme responsible for the synthesis of polyunsaturated phospholipids. Despite this deficiency in 18:1-desaturase activity, mutant plants contained relatively high levels of 18:3 in their leaf phospholipids. This finding is interpreted as additional evidence that considerable two-way exchange of lipid occurs between the chloroplast and endoplasmic reticulum and that this exchange allows the chloroplast desaturases to provide lipids containing 18:3 to the extrachloroplast compartment, thus partially alleviating the deficiency in 18:1 desaturase activity. << Less

  J. Biol. Chem. 267:1502-1509(1992) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• The role of cytochrome b5 in delta 12 desaturation of oleic acid by microsomes of safflower (Carthamus tinctorius L.).

  Kearns E.V., Hugly S., Somerville C.R.

  The electron donors for the membrane-bound fatty acid desaturases of higher plants have not previously been identified. In order to assess the participation of cytochrome b5 in microsomal fatty acid desaturation, the cytoplasmic domain of microsomal cytochrome b5 was purified from Brassica olerace ... >> More

  The electron donors for the membrane-bound fatty acid desaturases of higher plants have not previously been identified. In order to assess the participation of cytochrome b5 in microsomal fatty acid desaturation, the cytoplasmic domain of microsomal cytochrome b5 was purified from Brassica oleracea, and murine polyclonal antibodies were prepared. The IgG fraction from ascites fluid inhibited 62% of NADH-dependent cytochrome c reduction in safflower (Carthamus tinctorius L.) microsomes. These antibodies also blocked desaturation of oleic acid to linoleic acid in lipids of C. tinctorius microsomes by 93%, suggesting that cytochrome b5 is the electron donor for the delta 12 desaturase. << Less

  Arch Biochem Biophys 284:431-436(1991) [PubMed] [EuropePMC]

• Electron-transport components of the 1-acyl-2-oleoyl-sn-glycero-3-phosphocholine delta 12-desaturase (delta 12-desaturase) in microsomal preparations from developing safflower (Carthamus tinctorius L.) cotyledons.

  Smith M.A., Cross A.R., Jones O.T., Griffiths W.T., Stymne S., Stobart K.

  The major cytochrome in microsomal membrane preparations from developing seeds of safflower (Carthamus tinctorius, var High Linoleate), has a reduced-minus-oxidized difference spectrum characteristic of a b-type cytochrome, and was identified from its midpoint-potential (E'7.2) value as cytochrome ... >> More

  The major cytochrome in microsomal membrane preparations from developing seeds of safflower (Carthamus tinctorius, var High Linoleate), has a reduced-minus-oxidized difference spectrum characteristic of a b-type cytochrome, and was identified from its midpoint-potential (E'7.2) value as cytochrome b5. Cytochromes P-450 and P-420 were also present. The cytochrome b5 content of microsomal preparations from a number of oilseed species was found to be in the order of 200-300 pmol/mg of protein. The cytochrome b5 was reduced in the membrane preparations by NADH, demonstrating the presence of an NADH: cytochrome b5 reductase; NADPH was a less effective donor. Microsomal membranes catalysed the NAD(P)H-dependent conversion of radioactive oleate into linoleate, indicating acyl-CoA: lysophosphatidylcholine acyltransferase and 1-acyl-2-oleoyl-sn-glycero-3-phosphocholine delta 12-desaturase (delta 12-desaturase) activity. Desaturation of oleate to linoleate was unaffected by CO, but inhibited by CN-. The addition of oleoyl-CoA to the NADH-reduced membranes resulted in the CN(-)-sensitive partial re-oxidation of cytochrome b5, indicating that electrons from NADH were transferred to the site of desaturation via this cytochrome. The delta 12-desaturase in safflower, therefore, is CN(-)-sensitive and appears to require cytochrome b5 and NADH: cytochrome b5 reductase for activity. << Less

  Biochem J 272:23-29(1990) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Evidence for an oleoyl phosphatidylcholine desaturase in microsomal preparations from cotyledons of safflower (Carthamus tinctorius) seed.

  Slack C.R., Roughan P.G., Browse J.

  1. [14C]Oleoyl-CoA was metabolized rapidly and essentially completely by microsomal preparations from developing safflower (Carthamus tinctorius) cotyledons, and most of the [14C]oleate was incorporated into 3-sn-phosphatidylcholine. 2. In aerobic reaction mixtures containing NADH2 the [14C]oleate ... >> More

  1. [14C]Oleoyl-CoA was metabolized rapidly and essentially completely by microsomal preparations from developing safflower (Carthamus tinctorius) cotyledons, and most of the [14C]oleate was incorporated into 3-sn-phosphatidylcholine. 2. In aerobic reaction mixtures containing NADH2 the [14C]oleate in 3-sn-phosphatidylcholine was converted into [14C]linoleate without any change in the specific radioactivity of the lipid. Over a 60 min incubation period the extent of conversion of [14C]oleoyl phosphatidylcholine into [14C]linoleoyl phosphatidylcholine was generally greater than 60%. The rate of desaturation of endogenous [14C]oleoyl phosphatidylcholine labelled from [14C]oleoyl-CoA was much greater that of exogenous [14C]dioleoyl phosphatidylcholine the specific radioactivity of the oleoyl moiety of the lipid remained constant, indicating that labelled and unlabelled oleate were desaturated at the same rate. On this assumption an initial rate of desaturation of about 15 nmol of oleate desaturated/min per mumol of 3-sn-phosphatidylcholine was estimated. 4. [14C]Oleate esterified at positions 1 and 2 of both endogenous and exogenous 3-sn-phosphatidylcholine was desaturated. 5. Attempts to demonstrate the presence of an oleoyl-CoA desaturase in safflower microsomal fractions by the appearance of linoleoyl-CoA in reaction mixtures were inconclusive. << Less

  Biochem J 179:649-656(1979) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Characterization of a membrane-bound phospholipid desaturase system of candida lipolytica.

  Pugh E.L., Kates M.

  Several characteristics of the microsomal phospholipid desaturase of Candida lipolytica are described. The phospholipid desaturase reaction required molecular oxygen and reduced pyridine nucleotides as essential cofactors and was inhibited by cyanide but not by carbonmonoxide, indicating that it r ... >> More

  Several characteristics of the microsomal phospholipid desaturase of Candida lipolytica are described. The phospholipid desaturase reaction required molecular oxygen and reduced pyridine nucleotides as essential cofactors and was inhibited by cyanide but not by carbonmonoxide, indicating that it required cytochrome b5. Desaturation of both 1-acyl-2-[14-C]oleoyl-sn-glycero-3-phosphorylcholine and 1,2-di-[14C] oleoyl-sn-glycero-3-phosphorylcholine appeared to follow Michaelis-Menten kinetics, with apparent Km values of 2.5 10-minus 4 M and 9.5 10-minus 4 M, respectively. Desaturation of the di-[14C] oleoylphosphatidylcholine took place at both position-1 and position-2; the distearoyl or dielaidoyl phosphatidylcholines were not desaturated. Rate of desaturation of the 1=acyl-2-[14-C] oleoyl-glycerophosphorylcholine by microsomes from cold-grown cells was equal to or slightly less than that by microsomes from cells grown at the normal growth temperature of 25 degreesC, measured in the temperature range 10-30 degrees C. However, the rate of desaturation of [14-C]-oleoyl-CoA desaturase was greater with the microsomal preparation from cold-grown cells than with that from 25 degreesC grown cells. These data suggest that the observed increase of diunsaturated fatty acids in cold-grown cells may perhaps be explained by the increased activity of the oleoyl-CoA desaturase acting at the low temperature. << Less

  Biochim Biophys Acta 380:442-453(1975) [PubMed] [EuropePMC]