A COMPARATIVE STUDY OF THE METABOLISM OF DE NOVO SYNTHESIZED FATTY ACIDS FROM ACETATE AND GLUCOSE, AND EXOGENOUS FATTY ACIDS, IN SLICES OF RABBIT CEREBRAL CORTEX DURING DEVELOPMENT

Slices of rabbit cerebral cortex, from the foetal stage to the adult have been used to compare lipid synthesis from fatty acids synthesized de novo from [U-¹⁴C]glucose and [1-¹⁴C]acetate, with lipid synthesis from exogenous albumin-bound [1-¹⁴C]palmitate. Incorporation into cellular lipid has been determined in terms of DNA, protein, wet wt. of tissue and wet weight of whole brain. On a wet wt. basis, maximum incorporation of glucose carbon into lipid occurred in the foetal brain while lipid synthesis from acetate and palmitate was maximum at 4–14 days after birth. Glucose and acetate were incorporated into a diversity of lipids (with increasing amounts of phosphatidylcholine synthesized during maturation), while palmitate was incorporated into the free fatty acid and triglyceride fractions. A greater proportion of acetate was incorporated into fatty acids of chain-length longer than C16 compared with the incorporation of palmitate. However, on a molar basis de novo synthesized and exogenous palmitate were elongated, desaturated and incorporated into phospholipids at a similar rate, while exogenous palmitate was incorporated to a greater extent than de nova synthesized fatty acid into the triglyceride fraction. This difference in metabolism may be due to the different size of the non-esterified fatty acid pool in the two situations. At the period of their most active formation, the very long-chain fatty acids may be synthesized from a pool of the C18 series of fatty acids (saturated and monoenoic) not in equilibrium with the bulk of C₁₈ acids in cerebral lipids. This could be a pool of acyl groups derived from ethanolamine phospholipids.     

IDENTIFICATION AND PHYLOGENETIC IMPLICATIONS OF FATTY ACIDS AND STEROLS IN THREE GENERA OF AQUATIC PHYCOMYCETES

Allomyces macrogynus, A. arbuscula, A. javanicus, Allomyces male and female hybrid strains, Blastocladia ramosa and Monoblepharella sp. were examined for their fatty acid and sterol compositions by GLC and combined GLC/MS. All the organisms produce a range of fatty acids 12 to 20 carbon atoms in length. Palmitic, stearic, and arachidic acid represent the highest concentrations of saturated fatty acids; oleic, linoleic, and arachidonic acid the highest unsaturated fatty acids. B. ramosa synthesizes only two polyunsaturates, linoleic and linolenic, but Allomyces and Monoblepharella are capable of desaturation as far as arachidonic acid. Cholesterol is produced by all the isolates and is the dominant sterol in Allomyces. 24-Methyl and 24-ethyl derivatives of cholesterol are the dominant sterols of Monoblepharella. B. ramosa contains a more complex sterol mixture representing changes which occur in the formation of cholesterol from lanosterol: 24-dihydrolanosterol, 14α-methyl Δ⁸-cholestenol, Δ⁸⁽⁹⁾-cholestenol, 14α-methyl Δ⁷-cholestenol, Δ⁷-cholestenol and cholesterol. Δ⁷-cholestenol, 24-dihydrolanosterol, and 14α-methyl Δ⁸-choIestenol appear to be the major components. This is the first time that 14α-methyl Δ⁸ and 14α-methyl Δ⁷-cholestenol have been reported as naturally occurring sterols.     

FATTY ACIDS AND HYDROXY FATTY ACIDS IN THREE SPECIES OF FRESHWATER EUSTIGMATOPHYTES

The monocarboxylic fatty acids and hydroxy fatty acids of three species of freshwater microalgae—Vischeria punctata Vischer, Vischeria helvetica (Vischer et Pascher) Taylor, and Eustigmatos vischeri (Hulbert) Taylor, all from the class Eustigmatophyceae— were examined. Each species displayed a very similar distribution of fatty acids, the most abundant of which were 20:5n-3, 16:0, and 16:1n-7; C₁₈ polyunsaturated fatty acids were minor components. These fatty acid distributions closely resemble those found in marine eustigmatophytes but are quite distinct from those found in most other algal classes. These microalgae also contain long-chain saturated and unsaturated monohydroxy fatty acids. Two distinct types of hydroxy fatty acids were found: a series of saturated α-hydroxy acids ranging from C₂₄ to C₃₀ with a shorter series of monounsaturated α-hydroxy acids ranging from C₂₆ to C₃₀ together with a series of saturated β-hydroxy acids ranging from C₂₆ to C₃₀. The latter have not previously been reported in either marine or freshwater microalgae, although C₃₀ to C₃₄ midchain (ω-18)-hydroxy fatty acids have been identified in hydrolyzed extracts from marine eustigmatophytes of the genus Nannochloropsis, and C₂₂ to C₂₆ saturated and monounsaturated α-hydroxy fatty acids have been found in three marine chlorophytes. These findings have provided a more complete picture of the lipid distributions within this little studied group of microalgae as well as a range of unusual compounds that might prove useful chemotaxonomic markers. The functions of the hydroxy fatty acids are not known, but a link to the formation of the lipid precursors of highly aliphatic biopolymers is suggested.     

THE INCORPORATION OF [1-14C]ACETATE INTO UNESTERIFIED FATTY ACIDS IN RAT CEREBRAL CORTEX IN VIVO

—The incorporation of [1-¹⁴C]acetate into unesterified fatty acids and into the fatty acids of neutral glycerides and of phospholipids has been measured in rat cerebral cortex in vivo. The most rapid incorporation is seen in the unesterified fatty acids which have a turnover time of 5-6 min. It is suggested that unesterified fatty acids are precursors to neutral glycerides and phospholipids rather than being derived from them by lipase activity.     

THE INFLUENCE OF KINETIN AND ANTIMETABOLITES ON THE SYNTHESIS OF FATTY ACIDS IN LEAVES

Green leaf tissues contain relatively higher proportions of unsaturated fatty acids, especially α-linolenic acid, than do etiolated or senescent tissues. There appear to be developmental changes in the fatty acid composition of leaves during maturation and senescence. The normal rate of development of spinach (Spinacia oleracea L.) and bean (Phaseolus vulgaris L.) leaf tissues was altered by the application of kinetin and antimetabolites. Spinach was used for the kinetin studies and bean for the antimetabolite studies. Supposedly the kinetin retarded senescence and the antimetabolites retarded normal development. Special emphasis was placed on the incorporation of acetate into palmitate, the most abundant saturated fatty acid, and into linolenate, the most abundant unsaturated fatty acid. Kinetin does not enhance linolenate synthesis, but kinetin-treated tissues contain proportionately more linolenate. In contrast, tissues treated with antimetabolites contain proportionately less linolenate. Actinomycin-D and puromycin seem to have a greater effect on the synthesis of linolenate than on the synthesis of palmitate. Chloramphenicol does not have this same differential effect. The possible influence of antimetabolites on the synthesis of unsaturated fatty acids is discussed.     

RADIOLABELING STUDIES OF LIPIDS AND FATTY ACIDS IN NANNOCHLOROPSIS (EUSTIGMATOPHYCEAE), AN OLEAGINOUS MARINE ALGA1

The synthesis of fatty acids and lipids in Nannochloropsis sp. was investigated by labeling cells in vivo with [¹⁴C]-bicarbonate or [¹⁴C]-acetate. [¹⁴C]-bicarbonate was incorporated to the greatest extent into 16:0, 16:1, and 14:0 fatty acids, which are the predominant fatty acids of triacylglycerols. However, more than half of the [¹⁴C]-acetate was incorporated into longer and more desaturated fatty acids, which are constituents of membrane lipids. [¹⁴C]-acetate was incorporated most strongly into phosphatidylcholine, which rapidly lost label during a 5-h chase period. The label associated with phosphatidylethanolamine also decreased during the chase period, whereas label in other membrane lipids and triacylglycerol increased. The dynamics of labeling, along with information regarding the acyl compositions of various lipids, suggests that 1) the primary products of chloroplast fatty acid synthesis are 14:0, 16:0, and 16:1; 2) C₂₀ fatty acids are formed by an elongation reaction that can utilize externally supplied acetate; 3) phosphatidylcholine is a site for desaturation of C₁₈ fatty acids; and 4) phosphatidylethanolamine may be a site for desaturation of C₂₀ fatty acids.     

FATTY ACIDS,AMINO ACIDS,MINERAL CONTENTS,AND PROXIMATE COMPOSITION OF SOME BROWN SEAWEEDS1

This study was conducted to create a nutritional database on brown seaweeds and to popularize their consumption and utilization in Iran. The fatty acid contents, amino acids profiles, and certain mineral elements composition of some brown seaweeds, Padina pavonica (L.) Thivy, Dictyota dichotoma (Huds.) J. V. Lamour., and Colpomenia sinuosa (Mert. ex Roth) Derbés et Solier were determined. Total lipid content ranged from 1.46 ± 0.38 to 2.94 ± 0.94 g · 100 g^?1dry weight (dwt), and the most abundant fatty acids were C16:0, C18:1, C20:4 ω6, and C20:5 ω3. The unsaturated fatty acids predominated in all species and had balanced sources of ω3 and ω6 acids. Highest total polyunsaturated fatty acid (PUFA) levels occurred in C. sinuosa. The protein content of D. dichotoma was 17.73 ± 0.29 g · 100 g^?1dwt, significantly higher than the other seaweeds examined. Among amino acids essential to human nutrition, methionine (Met; in D. dichotoma and P. pavonica) and lysine (Lys; in C. sinuosa) were present in high concentrations. The crude fiber content varied by 9.5 ± 11.6 g · 100 g^?1dwt in all species. Chemical analysis indicated that ash content was between 27.02 ± 0.6 and 39.28 ± 0.7 g · 100 g^?1dwt, and that these seaweeds contained higher amounts of both macrominerals (7,308–9,160 mg · 100 g^?1dwt; Na, K, Ca) and trace elements (263–1,594 mg · 100 g^?1dwt; Fe, Ni, Mn, Cu, Co) than have been reported for edible land plants. C. sinuosa had the highest amount of Ca, Fe, and a considerable content of Na was measured in P. pavonica.     

METABOLISM OF BRAIN SPHINGOMYELINS: HALF-LIVES OF SPHINGOSINE, FATTY ACIDS AND PHOSPHATE FROM TWO TYPES OF RAT BRAIN SPHINGOMYELIN

Abstract— The metabolism of rat brain sphingomyelins containing short-chain (C₁₆-C₁₈) and long-chain (C₂₀- C₂₄) fatty acids has been studied by determination of the content of radioactivity in the sphingo-sinc. fatty acids and phosphate of the sphingomyelins over a period of 60 days following the intracisternal injection of [¹⁴C]acetate and [³²P]phosphate. From the rate of decrease of the specific radioactivities of the different constituents of short-chain fatty acid sphingomyelins, we have calculated a half-life of 65 days for sphingosine. 41 days for fatty acids and 62 days for phosphate. For the long-chain fatty acid sphingomyelins the half-life of sphingosine was approximately 465 days. The fatty acids and phosphate from these sphingomyelins had fast and slow turnover pools. The half-life for the fast pool was 7 days for the two constituents and the estimated half-lives for the slow pool were 220 days for fatty acids and 480 days for phosphate. These results suggest that one can distinguish at least three metabolic pools of brain sphingomyelins: (a) sphingomyelins with long-chain fatty acids situated in myelin whose half-lives are 465 days for sphingosine, 220 days for fatty acids and 480 days for phosphate; (b) sphingomyelins with long-chain fatty acids located mainly in non-myelin structures having half-lives of 465 days for sphingosine. 7 days for fatty acids and 7 days for phosphate; (c) sphingomyeiins with short-chain fatty acids with half-lives of 65 days for sphingosine. 41 days for fatty acids and 62 days for phosphate. The differences between the half-lives of the three metabolic pools of sphingomyelin, together with the subcellular localizations of the two molecular species of these compounds, suggest that the metabolism of the different molecular species of sphingomyelin are independent and that in various subcellular fractions the long-chain fatty acid and short-chain fatty acid sphingomyelins have different turnover rates.     

FATTY ACIDS OF CUPHEA (LYTHRACEAE) SEED LIPIDS AND THEIR SYSTEMATIC SIGNIFICANCE

Fatty acid analyses of seed lipids in 46 species of Cuphea are presented, representing the first major survey of a molecular nature for the family. A remarkable diversity in composition is found, with seeds containing high amounts of several medium chain fatty acids. Lauric acid (12:0) predominates in 43% of the species studied, constituting 50–74% of the total fatty acid content. Capric acid (10:0) is the dominant fatty acid in 32% of the species, comprising as much as 87% of the total acid content. Caprylic acid (8:0) predominates in one section of the genus. The emphasis on production of fatty acids with carbon chain lengths of 12, ten, and eight carbon atoms is unique among plant genera studied to date. Among seven of the nine sections studied, one pattern of fatty acid composition predominates. Two sections have no characteristic pattern, supporting other evidence of their polyphyletic origin. The most significant systematic contribution is made by comparison of the predominate fatty acid components in the seed lipids. When used in conjunction with floral morphology, pollen studies, and chromosome number, it provides an important new basis on which to draw inferences of evolution and clarify present relationships within the genus. Additionally, a trend from the longer-chained, unsaturated linoleic acid (18:2) as a major lipid component to shorter-chained saturated capric and caprylic acids is correlated with increasing floral specialization. It is suggested that mutations in regulatory genes have occurred which cause fatty acid production in seeds to cease at progressively earlier stages, resulting in accumulation of large amounts of single fatty acids of progressively shorter carbon chain lengths.     

STIMULATION OF FUNDULUS BY HYDROCHLORIC AND FATTY ACIDS IN FRESH WATER,AND BY FATTY ACIDS,MINERAL ACIDS,AND THE SODIUM SALTS OF MINERAL ACIDS IN SEA WATER

1. Fundulus heteroclitus was found to be a reliable experimental animal for studies on chemical stimulation in either fresh or sea water. 2. The response of Fundulus to hydrochloric, acetic, propionic, butyric, valeric, and caproic acids was determined in fresh water, while the same acids plus sulfuric and nitric, as well as the sodium salts of the mineral acids, were tested in sea water. 3. Stimulation of Fundulus by hydrochloric acid in fresh water is correlated with the effective hydrogen ion concentration. Stimulation by the n-aliphatic acids in the same environment is correlated with two factors, the effective hydrogen ion concentration and the potential of the non-polar group in the molecule. However, as the number of CH₂ groups increases the stimulating effect increases by smaller and smaller amounts, approaching a maximum value. 4. Stimulation of Fundulus by hydrochloric, sulfuric, and nitric acids in sea water is correlated with the forces of primary valence which in turn are correlated with the change in hydrogen ion concentration of the sea water. The n-aliphatic acids increase in stimulating efficiency in sea water as the length of the carbon chain increases, but a limiting value is not reached as soon as in fresh water. 5. Only a slight difference in stimulation by hydrochloric acid is found in sea water and in fresh water. However, there is a significant difference in stimulation by the fatty acids in fresh and in sea water, which is partly explained by the different buffering capacities of the two media. It is to be noted that in the same environment two different fish, Fundulus and Eupomotis, give different results, while the same fish (Fundulus) in two different environments responds similarly to mineral acids but differently to fatty acids. These results illustrate that stimulation is a function of the interaction between environment and receptors, and that each is important in determining the response. 6. Stimulation by sodium chloride, nitrate, and sulfate is correlated with equivalent concentrations of the salts added to sea water, or with the forces of primary valence. Although the threshold for stimulation by the salts is considerably higher than for the acids, the efficiency of stimulation by the salts is greater.     

PIGMENTS,FATTY ACIDS,AND STEROLS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM1

Cultures and field samples of the toxic dinoflagellate Gymnodinium catenatum Graham from Tasmania, Australia, were analyzed for pigment, fatty acid, and sterol composition. Gymnodinium catenatum contained the characteristic pigments of photosynthetic dinoflagellates, including chlorophyll a, chlorophyll c₂, and the carotenoids peridinin, dinoxanthin, diadinoxanthin, diatoxanthin, and β,β-carotene. In midlogarithmic and early stationary phase cultures, the chlorophyll a content ranged 50–72 pg · cell^?1, total lipids 956–2084 pg · cell^?1, total fatty acids 426–804 pg · cell^?1, and total sterols 8–20 pg · cell^?1. The major fatty acids (in order of decreasing abundance) were 16:0, 22:6(n-3), and 20:5(n-3) (collectively 65–70% of the total fatty acids), followed by 16:1(n-7), 18:2(n-6), and 14:0. This distribution is characteristic of most dinoflagellates, except for the low abundance (<3%) of the fatty acid 18:5(n-3), considered by some authors to be a marker for dinoflagellates. The three major sterols were 4α-methyl-5α-cholest-7-en-3β-ol, 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (the dinoflagellate sterol, dinosterol), and 4α,23,24-trimethyl-5α-cholest-7-en-3β-ol. These three sterols comprised about 75% of the total sterols in both logarithmic and early stationary phase cultures, and they were also found in high proportions (22–25%) in natural dinoflagellate bloom samples. 4-Desmethyl sterols, which are common in most microalgae, were only present in trace amounts in G. catenatum. The chemotaxonomic affinities of G. catenatum and the potential for using specific signature lipids for monitoring toxic dinoflagellate blooms are discussed.     

INCORPORATION AND METABOLISM OF THE DIETARY TRANS-UNSATURATED FATTY ACID,ELAIDIC ACID,BY DEVELOPING RAT BRAIN1

Trans-unsaturated fatty acids, geometrical isomers of naturally occurring cis-acids, are dietary components and are incorporated into complex lipids of many tissues. There is little information about incorporation into brain and effects on CNS functions. In our experiments, mixtures of [l-¹⁴C]-elaidic acid and [9,10-³H]oleic were injected intragastrically into a total of 34 rats at 6, 12 and 16 days of age. Animals were killed 4, 8, 24, 48 and 96 h after administration and brain and liver lipids analyzed. With all ages examined, about 0.02–0.22% of the administered radioactivity from each fatty acid was found in brain lipids with incorporation increasing with time after administration. Phospholipids accounted for 60–85% of the total label from both fatty acids; of this phospholipid label, 40–50%, of the ¹⁴C was in unaltered irans-monoene. Up to 22% of the total ¹⁴C label recovered from brain was in cholesterol. By contrast to brain, labeling of liver lipid was much greater and was highest at 4 h after administration; there was proportionally less ¹⁴C or ³H label in palmitate and cholesterol compared to brain. Thus, intact trans-fatty acid, elaidic acid, was incorporated into developing brain, but at slower rates than into liver. These studies establish that the developing central nervous system does not exclude dietary trans-acids.     

THE RELEASE OF BRAIN FREE FATTY ACIDS DURING ISCHAEMIA IN ESSENTIAL FATTY ACID-DEFICIENT RATS

—The release of free fatty acids and especially of free arachidonic acid occurring in rat brain during ischaemia has been studied in essential fatty acid-deficient animals. Free fatty acid levels are lower in essential fatty acid-deficient brains before and especially after 5 min of ischaemia. The percentage of arachidonic acid, in respect of total free fatty acids, is similar in both control and essential fatty acid-deficient brains before ischaemia (0 min), but is greatly reduced in deficient brains in respect of controls after ischaemia (5 min). Total levels of free arachidonic acid are thus greatly reduced after ischaemia in the brain of essential fatty acid-deficient rats. Focussed microwave irradiation of the brain, a technique which instantaneously kills the animals, and which was used for the determination of brain basal levels of free fatty acids and free arachidonic acid, does not per se modify brain lipid and fatty acid composition.     

STIMULATION BY MINERAL AND FATTY ACIDS IN THE BARNACLE BALANUS BALANOIDES

1. Stimulation in the rock barnacle Balanus balanoides by hydrochloric, sulfuric, and nitric acids, and by the first seven members of the normal aliphatic acid series has been studied. The hydrogen ion concentrations of the solutions tested varied from 3.2 x 10^–8 to 5.889 x 10^–6. The criterion of response was percentage closure in groups of individuals, recorded at 1 minute intervals until maximum closure occurred. 2. The intensity of stimulation by these acids is proportional to the effects of two forces, one related to the change in the (H⁺), and the other to the field of force around the anion of the acid added to the environment. 3. A preliminary interpretation of the results led to the development of the following expression which fits approximately the data obtained at the end of 4 minutes: Per cent closure = 100 – 100e ^{–0.1z+(0.003125)2–0.1z+(0.003125)2n(z–0.4)} where z is the (H⁺) x 10⁷ and n is the number of carbon atoms (if present) in the anion of the acid. This equation assumes that the anions of the mineral acids enter into the reaction stoichiometrically, and emphasizes the difference in the fields of force around the anion of the fatty acids, a difference which is correlated with the length of the carbon chain. 4. A further analysis of the data revealed the presence of three or more receptor groups which appeared to be differentially affected by forces originating from the anions of the acids. 5. The order of stimulating efficiency for the mineral acids was found to be: HCl>H₂SO₄>HNO₃. 6. The order of stimulating efficiency for the fatty acids was found to be: heptylic>caproic>valeric>butyric = acetic>propionic = formic.     

INFLUENCE OF IRRADIANCE ON THE FATTY ACID COMPOSITION OF PHYTOPLANKTON1

Eight species of marine phytoplankton commonly used in aquaculture were grown under a range of photon flux densities (PEDs) and analyzed for their fatty acid (FA) composition. Fatty and composition changed considerably at different PFDs although no consistent correlation between the relative proportion of a single FA and μ or chl a · cell^?1 was apparent. Within an individual species the percentage of certain fatty acids covaried with PFDs, growth rate and/or chl a · cell^?1. The light conditions which produced the greatest proportion of the essential fatty acids was species specific. Eicosapentaenoic acid. 20:5ω3 increased from 6.1% to 15.5% of the total fatty acids of Chaetoceros simplex Ostenfield grown at PFDs which decreased from 225 μE · m^?2· s^?1 to 6 μE · m^?2· s^?1, respectively. Most species had their greatest proportion of 20: 5ω3 at low levels of irradiance. Conversely, docosahexaenoic acid, 22:6ω3, decreased from 9.7% to 3.6% of the total fatty acids in Pavlova lutheri Droop as PFD decreased. The percentage of 22:6ω3 generally decreased with decreasing irradiances. In all diatoms the percentage of 16:0 was significantly correlated with PFD, and in three of five diatoms, with growth rate (μ). Results suggest that fatty acid composition is a highly dynamic component of cellular physiology, which responds significantly to variation in PFD.     

IN VIVO STUDIES ON THE METABOLISM OF [15,16-3H]TETRACOSANOIC ACID (LIGNOCERIC ACID) IN ADULT RAT BRAIN

—Adult rats were killed 16 h, 48 h, 6 days and 21 days after intracerebral application of n-[15,16-³H]tetracosanoic acid (lignoceric acid). After incorporation into complex lipids with a strong preference for the ester-bound fatty acids of glycerophospholipids, radioactivity decreased with time. The incorporated activity into the amide-bound fatty acids of sphingolipids was also shown to decrease, with exception of the cerebroside of the hydroxy fatty acid type (cerebron fraction). Only negligible amounts of labelled triglyceride and cholesterol ester could be detected. The fatty acids derived from the complex lipids were analysed by radio gas chromatography. It was revealed that some of the applied labelled lignoceric acid was hydroxylated and incorporated into the cerebron fraction while the rest had their chains shortened. In the latter case all even and odd numbered chain lengths down to C₁₈ and C₁₆ (stearic and palmitic acid) were detected. At this stage, the pool of the degradation products of lignoceric acid is stabilized by the preferred incorporation of fatty acids of these chain lengths into glycerophospholipids. A time-dependent desaturation to oleic acid from stearic acid was observed.     

RENEWAL OF FATTY ACIDS IN THE MEMBRANES OF VISUAL CELL OUTER SEGMENTS

The renewal of fatty acids in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids. Most of the radioactive material could be extracted from the retina with chloroform-methanol, indicating that the fatty acids had been esterified in lipids. Analysis of the extracts, after injection of [³H]palmitic acid, revealed that the radioactivity was predominantly in phospholipid. Palmitic acid was initially concentrated in the pigment epithelium, particularly in oil droplets which are storage sites for vitamin A esterified with fatty acid. The cytoplasm, but not the nucleus of these cells, was also heavily labeled. Radioactive fatty acid was bound immediately to the visual cell outer segment membranes, including detached rod membranes which had been phagocytized by the pigment epithelium. This is believed to be due to fatty acid exchange in phospholipid molecules already situated in the membranes. Gradually, the concentration of radioactive material in the visual cell outer segment membranes increased, apparently as a result of the addition of new phospholipid molecules, possibly augmented by the transfer from the pigment epithelium of esterified vitamin A. Injected fatty acid became particularly concentrated in new membranes which are continually assembled at the base of rod outer segments. This localized concentration was short-lived, apparently due to the rapid renewal of fatty acid. The results support the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement, including fatty acid exchange and replacement of phospholipid molecules in existing membranes.     

FATTY ACIDS IN PHOTOTROPHIC AND MIXOTROPHIC GYRODINIUM GALATHE‐ANUM (DINOPHYCEAE)

Fatty acids were measured in G. galatheanum grown either phototrophically, or mixotrophically with Storeatula major (Cryptophyceae) as prey. G. galatheanum, like many photosynthetic dinoflagellates, contains high amounts of n‐3 long‐chain‐polyunsaturated fatty acids (LC‐PUFA) such as docosahexaenoic acid (DHA, 22:6n‐3) and the hemolytic toxic fatty acid 18:5n‐3. We hypothesize that a benefit of phagotrophy in G. galatheanum is the acquisition of precursor linolenic acid (18:3n‐3) that fuels LC‐PUFA synthesis. Phototrophs grew at 0.37 d^?1, while mixotrophs grew at 0.40 d^?1 with a feeding rate of 0.62 d^?1. Photosynthesis was lower in mixotrophs (3.7 pg C cell^?1 h^?1) than phototrophs (4.9 pg C cell^?1 h^?1). DHA levels were higher in mixotrophs [3.7 (+/? 0.11) pg cell^?1] than phototrophs [3.0 (+/? 0.16) pg cell^?1] and prey [0.4 (+/? 0.01) pg cell^?1]. 18:5n–3 levels [1.7 (+/? 0.03) pg cell^?1] were similar in phototrophs and mixotrophs. An intermediate in n‐3 LC‐PUFA synthesis, 20:4n‐3, accumulated in mixotrophs [0.6 (+/? 0.27) pg cell^?1] relative to phototrophs (not detected) and prey [0.03 (+/? 0.002) pg cell^?1]. Low ratios of linolenic acid to DHA in phototrophic G. galatheanum (0.14) relative to mixotrophic G. galatheanum (0.29) and prey (2.14) are consistent with substrate limitation of LC‐PUFA synthesis in phototrophs. Accumulation of 20:4n‐3 suggests incomplete conversion of linolenic acid to DHA, possibly due to conditions in batch culture. We conclude that precursors for n‐3 LC‐PUFA biosynthesis in G. galatheanum may be acquired through ingestion of S. major, and may partially control feeding/photosynthesis in mixotrophic populations.     

FATTY ACIDS IN LOTIC PERIPHYTON: ANOTHER MEASURE OF COMMUNITY STRUCTURE1

The fatty acid spectra of 6 periphyton communities developed in laboratory streams at different combinations of light intensity and current velocity were determined by gas-liquid chromatography and silver nitrate thin-layer chromatography. Differences in species composition of the communities apparently had no striking effect on proportions of palmitic and stearic acids, whereas concentrations of myristic, palmitoleic, oleic, linoleic, and linolenic acids and a C_20:5 acid were more closely related to taxonomic differences. In general, communities dominated by blue-green algae exhibited relatively high proportions of oleic, linolenic, and linolenic acids and low proportions of palmitoleic acid and a C_20:5 acid, as compared to communities consisting primarily of diatoms. The data also indicated an inverse relationship between fatty acid redundancy and species diversity.     

ACTIVATION OF GUANYLATE CYCLASE IN SYNAPTIC PLASMA MEMBRANES OF CEREBRAL CORTEX BY FREE FATTY ACIDS

Guanylate cyclase (EC 4.6.1.2) of synaptic plasma membranes of rat cerebral cortex was stimulated about 6-fold by several unsaturated fatty acids (arachidonic, linolenic, linoleic, oleic, palmitoleic and myristoleic acid). Ricinoleic acid (12-hydroxyoleic acid) was much less effective. Saturated fatty acids (C₁₀ and C₁₄-C₂₀) and the methylester of linoleic acid were ineffective. Stimulation by linoleic acid was influenced by the concentration of enzyme protein. At 480 μg/ml of protein 0.6 mm -linoleic acid produced maximal activation of 6-fold_ Activity stimulated by linoleic acid examined with 1.0 mm -GTP was maximal at pH 7.8-7.9 and with 2 mm -MnCl₂, whereas basal activity showed broad optimal pH and Mn²⁺-concentration dependence. Activation of the enzyme by linoleic acid was only partially reversed by washing. Particulate guanylate cyclase of heart, small intestine, adrenal medulla, liver and lung was also activated by linoleic acid. The extents of activation (1.5-14.7-fold) by linoleic acid and the concentrations (0.2-1.0 mat) required for maximal activation depended on the tissues.