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R L Conner

Publications and source records attributed to R L Conner.

At least 37 records · Page 2Linked to original sources
PubMed1979

Positional distribution of fatty acids in the glycerophospholipids of Tetrahymena pyriformis.

The positional distributions of the fatty acids in the major glycerophospholipids of Tetrahymena pyriformis W were analyzed. A comparison was made of the acyl distributions in normal and ergosterol-grown cells. It was assumed that the positional arrangement of fatty acids would serve as an indicator of acyltransferase enzyme specificity. The acyltransferases in this protozoan have substrate specificities that direct unsaturated groups, particularly polyunsaturates, to the 2-carbon of the glycerophospholipids. An exception is gamma-linolenic acid, which represents a substantial proportion of the total acids at both carbons. Saturated and iso-acids are esterified primarily at the 1-carbon. The qualitative pattern of the fatty acyl distribution is the same in both normal and ergosterol-grown organisms. Sterol substitution produces quantitative differences in the acyl components at both the 1- and 2-carbons of the glycerophospholipids. These differences include a shortening of the average chain length and a decrease in total unsaturation at both the 1- and 2-positions. In addition, there is a modification at the 2-carbon in the relative amounts of the products of two pathways involved in the biosynthesis of fatty acids. The data are interpreted to indicate that the fatty acid transformations in the glycerophospholipids of organisms that contain ergosterol are not the result of altered acyltransferase specificities.

Acyltransferases↗
PubMed1976

Unsaturated fatty acid biosynthesis in Tetrahymena. Evidence for two pathways.

The ciliate Tetrahymena pyriformis synthesizes a wide variety of saturated and unsaturated fatty acids. Variations in growth temperature or the addition of sterols such as cholesterol or ergosterol alter the proportions of a number of unsaturated fatty acids. The pattern of substitution is complex when examined on the basis of individual fatty acids. A straightforward explanation is possible, however, if biosynthetic groupings are considered. Stearic acid gives rise to oleic, linoleic, and gamma-linolenic acids as shown by others. The environmental parameters influence the amounts of the unsaturated derivatives of stearic acid as a group and result in an increase or decrease in all members of this biosynthetic family in a fashion that depends on a particular set of conditions. The replacement of the stearate derivatives by unsaturated components that are derived from palmitic acid has been demonstrated. The addition of radiolabeled palmitic, palmitoleic, or stearic acids to the cells when coupled with radioisotope distribution measurements, isolation, and characterization of the acids, and the refeeding of key intermediates substantiates a second biosynthetic scheme for the synthesis of unsaturated acids in this ciliate. This novel pathway yields an unusual fatty acid, 18:2 delta6,11, as a major terminal product. Plamitic acid is the precursor for the members of both sequences. Palmitoleic acid can be desaturated further to produce two hexadecadienoates and a hexadecatrienoate. Further, palmitoleic acid (16:1 delta9) is elongated to cis-vaccenic acid (18:1 delta11) which is then desaturated to 18:2 delta6,11. Linoleic and gamma-linolenic acids were essentially unlabeled when [14C]palmitoleic acid was provided. Refeeding radiolabeled 18:2 delta6,11 to the cells revealed the extensive incorporation of this acid into the polar lipids and the absence of additional metabolites. [14C]Stearic acid addition to the cells results in extensive labeling of linoleic and gamma-linolenic acids, but not of 18:2 delta6,11. These observations confirm the existence of alternative and separate pathways for the synthesis of unsaturated fatty acids.

Animals↗
PubMed1976

The effect of temperature on the fatty acid composition of Tetrahymena pyriformis WH-14.

A reduction in the growth temperature of Tetrahymena pyriformis strains WH-14 from 35 C to 15 C resulted in distinct alterations in the fatty acid composition of the glycerophospholipids. The proportion of normal saturated acids declined from 26 to 19%; palmitoleic acid increased by 6%, and the composition of the polyunsaturated fatty acids increased in 18:2 delta 6,11 (n) and decreased in 18:2 delta 9,12 (n) and 18:3 delta 6,9,12 (n). The unsaturation index (the average number of double bonds/100 molecules) did not change with a shift in temperature.

Animals↗
PubMed1975

Effect of sterol replacement in vivo on the fatty acid composition of Tetrahymena.

The addition of ergosterol to cultures of Tetrahymena pyriformis results in (a) the accumulation of the sterol by the cells; (b) the inhibition of the synthesis of the pentacyclic triterpenoid alcohol, tetrahymanol; (c) the replacement of tetrahymanol by ergosterol in the ciliate membranes. The dry weight and lipid content of sterol-supplemented ciliates did not differ from the controls. Examination of the lipid classes revealed no change in composition except for a higher content of ergosterol in supplemented cells than tetrahymanol in control cultures. The relative proportions of triglycerides, the major classes of polar lipids, 1-alkyl phospholipids and phosphonolipids, appeared unaltered. A complex array of fatty acids is found in this ciliate. Several acids not reported previously in this organism were isolated and identified, and the novel fatty acid 18:2 delta 6, 11, was found in substantial amounts. Ergosterol supplementation altered the proportions of the fatty acids, although not all lipid classes were affected to the same extent. The changes noted were of three general types: (a) a shortening of the fatty acyl chain length in the acids of the normal series; (b) a lowering in the degree of unsaturation; (c) a discrimination between two isomers of lionoleate, 18:2 delta 6, 11 and 18:2 delta 9, 12. The former is elevated in the presence of ergosterol while the latter is depressed. Each class of polar lipids has a distinctive fatty acid composition. Among the glycerophospholipids, cardiolipin and phosphatidylcholine were least affected, while the mixture of 1-alkyl-2-acyl-sn-glycero-3-(2-aminoethyl)-phosphonate and 1,2-diacyl-sn-glycero-3-(2-aminoethyl)-phosphonate was most markedly altered. Sphingolipid fatty acid composition was influenced by ergosterol supplementation. Two changes were noted: (a) a reduction in the length of the hydrocarbon chain; (b) an increase in the proportion of alpha-hydroxy acids. The impact of ergosterol on the fatty acid composition of the polar lipids may be on fatty acid biosynthesis, on incorporation of fatty acids, or on the turnover rates of the fatty acyl groups. Ergosterol is concentrated in the ciliary (limiting) membrane, as are the polar lipids most affected. This localization allows the speculation that the change in fatty acid composition may be related to the maintenance of optimal membrane properties upon the introduction of the sterol.

Animals↗
PubMed1975

The effects of isovalerate supplementation on growth and fatty acid composition of Tetrahymena pyriformis W.

Cultures of Tetrahymena pyriformis W respond to isovalerate supplementation by an increase in odd-numbered saturated, unsaturated and alpha-hydroxy iso-fatty acids and by a decrease in even-numbered normal fatty acids in the glycerolipids and sphingolipids. Supplementation, however, did not alter the relative amount of unsaturated fatty acids found in the polar lipids. The unsaturated acids 17 : 1(i) and 19 : 1(i) were isolated from cells grown with [1-14C]isovalerate and found to have a higher specific activity than the monoenes of the normal series. Isotopic and gas-chromatographic analyses also indicated the presence of dienoic and trienoic acids of the iso-acid series. The iso-fatty acid content was elevated with isovalerate levels up to 5.0 mM and an inhibition of growth was noted. At higher concentrations of the short chain precursor, no further increase in total cellular iso-acids was detected although growth inhibition was more pronounced. The alpha-hydroxy iso-fatty acids of the sphingolipids, however, were elevated in a fashion that paralleled the external concentration of isovalerate; thus, the amount of alpha-hydroxy iso-acids and the degree of growth inhibition show a direct relationship. The increase in alpha-hydroxy iso-acid content of the sphingolipids was at the expense of the saturated normal and iso-acid components. The impact on the physiology of the cells can be envisaged as the result of changes in membrane fluidity due to the presence of high levels of iso-fatty acids without an accompanying reduction in unsaturated acids.

Fatty Acids↗