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PubMed1982

Cholesterol biosynthesis and modulation of membrane cholesterol and lipid dynamics in rat intestinal microvillus membranes.

Experiments were performed to test the hypothesis that cholesterol biosynthesis in the rat ileal enterocyte, the major absorptive cell lining the distal epithelium of the small intestine, can modulate the cholesterol content and the motional freedom of the plasma membrane lipids. Decreased sterol biosynthesis in vivo was elicited by feeding sodium taurocholate or by fasting the rats, whereas increased synthesis was induced by biliary ligation or feeding cholestyramine, a bile salt binding resin; these effects were monitored by assay of mucosal 3-hydroxy-3-methylglutaryl coenzyme A reductase. After each procedure, isolated microvillus membranes were examined to determine the lipid composition and the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. The results demonstrate that variations in cholesterol biosynthesis in vivo can modulate the cholesterol content and the motional freedom of the lipids of the microvillus membrane; similar effects were not observed on the basolateral membrane. The observations suggest that the normal pattern of decreased lipid motional freedom in microvillus membranes of the distal as compared to the proximal small intestine of the rat results from higher rates of cholesterol biosynthesis in the distal mucosa.

Animals↗

PubMed1975

Biosynthesis of bacterial menaquinones. Menaquinone mutants of Escherichia coli.

The isolation of six menaquinone mutants of Escherichia coli is described. It was shown that the mutants fall into two genetic classes. The first class carries mutations in a gene designated menA, which was located at minute 78 on the E. coli chromosome by cotransduction with the glpK and metB genes. The second class carries mutations in a gene designated menB. It was shown that this gene was not cotransducible with the menA gene. The biosynthesis of menaquinone in E. coli was studied using a variety of mutants blocked in aromatic biosynthesis together with the two classes of menaquinone mutants. It was demonstrated that chorismate is the branch point compound leading to menaquinone, and that 2-succinylbenzoic acid and 1,4-dihydroxy-2-naphthoic acid can serve as menaquinoone precursors in E. coli. It was also shown that menA- and menB- strains accumulate 1,4-dihydroxy-2-naphthoic acid and 2-succinylbenzoic acid, respectively, in their culture supernatants. The accumulation of the two compounds by the mutants together with their activity as menaquinone precursors provide strong evidence that they ar true intermediates in menaquinone biosynthesis. A pathway is proposed for the biosynthesis of bacterial menaquinones in which each intermediate has been adequately characterized.

Benzyl Compounds↗

PubMed2004

In vitro biosynthesis of glycosylphosphatidylinositol in Aspergillus fumigatus.

Glycosylphosphatidylinositol (GPI) represents a mechanism for the attachment of proteins to the plasma membrane found in all eukaryotic cells. GPI biosynthesis has been mainly studied in parasites, yeast, and mammalian cells. Aspergillus fumigatus, a filamentous fungus, produces GPI-anchored molecules, some of them being essential in the construction of the cell wall. An in vitro assay was used to study the GPI biosynthesis in the mycelium form of this organism. In the presence of UDP-GlcNAc and coenzyme A, the cell-free system produces the initial intermediates of the GPI biosynthesis: GlcNAc-PI, GlcN-PI, and GlcN-(acyl)PI. Using GDP-Man, two types of mannosylation are observed. First, one or two mannose residues are added to GlcN-PI. This mannosylation, never described in fungi, does not require dolichol phosphomannoside (Dol-P-Man) as the monosaccharide donor. Second, one to five mannose residues are added to GlcN-(acyl)PI using Dol-P-Man as the mannose donor. The addition of ethanolamine phosphate groups to the first, second, and third mannose residue is also observed. This latter series of GPI intermediates identified in the A. fumigatus cell-free system indicates that GPI biosynthesis in this filamentous fungus is similar to the mammalian or yeast systems. Thus, these biochemical data are in agreement with a comparative genome analysis that shows that all but 3 of the 21 genes described in the Saccharomyces cerevisiae GPI pathways are found in A. fumigatus.

Acetylglucosamine↗

PubMedDate not supplied

Metabolic engineering of pentose phosphate pathway in Ralstoniaeutropha for enhanced biosynthesis of poly-beta-hydroxybutyrate.

Poly-beta-hydroxybutyrate (PHB) biosynthesis in Ralstonia eutropha from gluconate as a carbon source is carried out through the Entner-Doudoroff (ED) pathway and the pentose-phosphate (PP) pathway generating NADPH and glyceraldehyde-3-phosphate that flows to acetyl-CoA, actively in the unbalanced PHB accumulation phase. The gnd gene encoding 6-phosphogluconate dehydrogenase (6PGDH) and the tktA gene encoding the transketolase (TK) in PP pathway of E. coli were transformed into R. eutropha H16 to modify the metabolic flux of gluconate to the PHB biosynthesis. Over-generated NADPH by the amplified gnd gene tended to depress the cell growth and PHB concentration. Meanwhile, the amplified tktA gene significantly increased both PHB biosynthesis and cell growth as a result of the effective flow of glyceraldehyde-3-phosphate into acetyl-CoA along with the concomitant supplementation of NADPH. The amplified tktA gene also activated the enzyme activities directly associated with PHB biosynthesis. The transformant R. eutropha harboring tktA gene was cultivated using pH-stat-fed-batch to achieve the overproduction of PHB.

Cell Culture Techniques↗

PubMedDate not supplied

Precursor and cofactor as a check valve for cephamycin biosynthesis in Streptomyces clavuligerus.

The biosynthesis of secondary metabolites is closely linked to primary metabolism via the supply of precursors, cofactors, and cellular energy. The availability of these precursors and cofactors can potentially be rate-limiting for secondary metabolism. A combined experimental and kinetic modeling approach was used to examine the regulation of flux in the cephamycin biosynthetic pathway in Streptomyces clavuligerus. The kinetic parameters of lysine 6-aminotransferase (LAT), the first enzyme leading to cephamycin biosynthesis and one which was previously identified as being a rate-limiting enzyme, were characterized. LAT converts lysine to alpha-aminoadipic acid using alpha-ketoglutarate as a cosubstrate. The K(m) values for lysine and alpha-ketoglutarate were substantially higher than those for their intracellular concentrations, suggesting that lysine and alpha-ketoglutarate may play a key role in regulating the flux of cephamycin biosynthesis. The important role of this precursor/cosubstrate was supported by simulated results using a kinetic model. When the intracellular concentrations and high K(m) values were taken into account, the predicted intermediate concentration was similar to the experimental measurements. The results demonstrate the controlling roles that precursors and cofactors may play in the biosynthesis of secondary metabolites.

Biotechnology↗

PubMed2002

Nonactin biosynthesis: the initial committed step is the condensation of acetate (malonate) and succinate.

Nonactin is a macrotetrolide antibiotic produced by Streptomyces griseus subsp. griseus ETH A7796 that has shown activity against the P170-glycoprotein efflux pump associated with multiple drug resistant cancer cells. Nonactin is a polyketide, albeit a highly atypical one. The structure is composed of two units of each of the enantiomers of nonactic acid, arranged in a macrocycle, so that the molecule has S4 symmetry and is achiral. The monomer units, (+)- and (-)-nonactic acid, are derived from acetate, succinate, and propionate, although the exact details of the assembly process are quite unclear. We have used feeding experiments with a series of multiple stable isotope labeled precursors to elucidate the details of the first committed step of nonactic acid biosynthesis. We have found that the (13)C label from 3-ketoadipate is incorporated specifically into both nonactic acid and its homologue, homononactic acid. The data conclusively show that the first committed step of nonactin biosynthesis is the coupling of a succinate derivative with either acetate or malonate. The differentiation into either nonactate or homononactate occurs after the initial condensation; the homologues are not derived from use of a different "starter unit" by the nonactate polyketide synthase. The first step of nonactin biosynthesis involves achiral intermediates; differentiation between the known enantiocomplementary biosynthesis pathways to form each enantiomer of the precursor monomer units likely occurs after the initial condensation reaction.

Anti-Bacterial Agents↗

PubMed2003

The complete gene cluster of the antitumor agent gilvocarcin V and its implication for the biosynthesis of the gilvocarcins.

Gilvocarcin V, an antitumor agent produced by the bacterium Streptomyces griseoflavus Gö 3592, is the most studied representative of the distinct family of benzo[d]naphtho[1,2-b]pyran-6-one aryl C-glycoside antibiotics, which show excellent antitumor activity and a remarkably low toxicity. Its biosynthesis contains many intriguing steps, including an oxidative rearrangement, the C-glycosylation, and the generation of a vinyl side chain. These steps all contribute to structural elements of the drug, which are essential for its biological activity, but only poorly understood. Herein we report the cloning and characterization of the gilvocarcin (gil) gene cluster from S. griseoflavus Gö 3592, and its heterologous expression in a foreign host (S. lividans). This is the first reported gene cluster encoding the biosynthesis of a benzo[d]naphtho[1,2-b]pyran-6-one aryl C-glycoside antibiotic, which not only provides insights regarding the biosynthesis of gilvocarcin V but also lays the foundation for the detailed studies of its intriguing biosynthetic steps and possibly for the generation of gilvocarcin analogues with improved biological activities through combinatorial biosynthesis.

Aminoglycosides↗

PubMed2004

Identification of a cluster of genes that directs desferrioxamine biosynthesis in Streptomyces coelicolor M145.

Desferrioxamines are a structurally related family of tris-hydroxamate siderophores that form strong hexadentate complexes with ferric iron. Desferrioxamine B has been used clinically for the treatment of iron overload in man. We have unambiguously identified desferrioxamine E as the major desferrioxamine siderophore produced by Streptomyces coelicolor M145 and have identified a cluster of four genes (desA-D) that directs desferrioxamine biosynthesis in this model actinomycete. On the basis of comparative sequence analysis of the proteins encoded by these genes, we propose a plausible pathway for desferrioxamine biosynthesis. The desferrioxamine biosynthetic pathway belongs to a new and rapidly emerging family of pathways for siderophore biosynthesis, widely distributed across diverse species of bacteria, which is biochemically distinct from the better known nonribosomal peptide synthetase (NRPS) pathway used in many organisms for siderophore biosynthesis.

Deferoxamine↗

PubMed2002

A specific and potent inhibitor of brassinosteroid biosynthesis possessing a dioxolane ring.

Screening for brassinosteroid biosynthesis inhibitors was performed to find azole derivatives that induced dwarfism, to resemble brassinosteroid-deficient mutants in Arabidopsis, and which could be rescued by brassinosteroid. Through this screening experiment, propiconazole fungicide was selected as a likely inhibitor of brassinosteroid biosynthesis and, thus, propiconazole derivatives with optimized activity and selectivity were synthesized. The biological activity of these compounds was evaluated by examining cress stem elongation. Among the compounds tested, 2RS,4RS-1-[2-(4-trifluoromethylphenyl)-4-n-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole (12) showed the most potent capability to retard cress stem elongation in the light. The compound-induced hypocotyl dwarfism was restored by the coapplication of 10 nM brassinolide but not by 1 microM gibberellin. These results suggest that 12 should affect brassinosteroid biosynthesis. The potency and specificity of 12 were greater than those of brassinazole, a previously reported brassinosteroid biosynthesis inhibitor.

Brassinosteroids↗

PubMed2004

The methylerythritol phosphate pathway contributes to carotenoid but not phytol biosynthesis in Euglena gracilis.

The biosynthesis of diadinoxanthin and beta-carotene in Euglena gracilis was examined using [1-13C]-D-glucose and [5,5-2H2]-1-deoxy-D-xylulose. In contrast to previous studies on isoprenoid biosynthesis in E. gracilis, the results demonstrate a role for the methylerythritol phosphate (MEP) pathway, along with the mevalonate pathway, in carotenoid biosynthesis. Interestingly, the MEP pathway is not involved in the biosynthesis of phytol, a result not previously observed for other chloroplast-containing organisms.

Animals↗

PubMedDate not supplied

The use of recombinant DNA techniques to study tylosin biosynthesis and resistance in Streptomyces fradiae.

A substantial amount of information on the biosynthesis of tylosin has been obtained over the past ten years. Physiological studies and experiments with tylosin-blocked (tyl) mutants have suggested the probable pathway by which tylactone is converted to tylosin. The development of recombinant DNA methodology for streptomycetes in general, and for Streptomyces fradiae in particular, has allowed us to apply gene cloning techniques in further studies of tylosin biosynthesis in S. fradiae. The macrocin O-methyltransferase (MOMT), which catalyzes the last step in tylosin biosynthesis, was purified, and the sequence of the 35 amino acids at its amino-terminus was determined. A synthetic 44 base oligonucleotide probe was constructed on the basis of the amino acid sequence. The probe was used to identify sequences containing the MOMT structural gene in bacteriophage and cosmid libraries of S. fradiae DNA. Complementation of tyl mutants with the cloned DNA sequences identified nine tyl biosynthetic genes (tylC, D, E, F, H, J, K, L, and M) in a 42 kb stretch of DNA. Genes complementing four mutant classes, tylA, B, G, and I were not found. A tylosin-resistance gene, tlrB, was located just left of the tyl gene cluster. Tylosin-sensitive mutants of S. fradiae, which were isolated from regenerated protoplasts and which have pleiotropic deficiencies in tylosin biosynthesis, contained deletions which included at least some of the identified tyl loci and one or both of two tylosin-resistance genes, tlrB and tlrC. Possible schemes for the functional organization of the tyl region of the S. fradiae genome are discussed.

DNA, Bacterial↗

PubMed1998

Cloning of three A-type cytochromes P450, CYP71E1, CYP98, and CYP99 from Sorghum bicolor (L.) Moench by a PCR approach and identification by expression in Escherichia coli of CYP71E1 as a multifunctional cytochrome P450 in the biosynthesis of the cyanogenic glucoside dhurrin.

A cDNA encoding the multifunctional cytochrome P450, CYP71E1, involved in the biosynthesis of the cyanogenic glucoside dhurrin from Sorghum bicolor (L.) Moench was isolated. A PCR approach based on three consensus sequences of A-type cytochromes P450- (V/I)KEX(L/F)R, FXPERF, and PFGXGRRXCXG-was applied. Three novel cytochromes P450 (CYP71E1, CYP98, and CYP99) in addition to a PCR fragment encoding sorghum cinnamic acid 4-hydroxylase were obtained. Reconstitution experiments with recombinant CYP71E1 heterologously expressed in Escherichia coli and sorghum NADPH-cytochrome P450-reductase in L-alpha-dilaurylphosphatidyl choline micelles identified CYP71E1 as the cytochrome P450 that catalyses the conversion of p-hydroxyphenylacetaldoxime to p-hydroxymandelonitrile in dhurrin biosynthesis. In accordance to the proposed pathway for dhurrin biosynthesis CYP71E1 catalyses the dehydration of the oxime to the corresponding nitrile, followed by a C-hydroxylation of the nitrile to produce p-hydroxymandelonitrile. In vivo administration of oxime to E. coli cells results in the accumulation of the nitrile, which indicates that the flavodoxin/flavodoxin reductase system in E. coli is only able to support CYP71E1 in the dehydration reaction, and not in the subsequent C-hydroxylation reaction. CYP79 catalyses the conversion of tyrosine to p-hydroxyphenylacetaldoxime, the first committed step in the biosynthesis of the cyanogenic glucoside dhurrin. Reconstitution of both CYP79 and CYP71E1 in combination with sorghum NADPH-cytochrome P450-reductase resulted in the conversion of tyrosine to p-hydroxymandelonitrile, i.e. the membranous part of the biosynthetic pathway of the cyanogenic glucoside dhurrin. Isolation of the cDNA for CYP71E1 together with the previously isolated cDNA for CYP79 provide important tools necessary for tissue-specific regulation of cyanogenic glucoside levels in plants to optimize food safety and pest resistance.

Amino Acid Sequence↗

PubMed2000

A cluster of genes for the biosynthesis of spinosyns, novel macrolide insect control agents produced by Saccharopolyspora spinosa.

Spinosyns A and D are the active ingredients in a family of insect control agents produced by fermentation of Saccharopolyspora spinosa. Spinosyns are 21-carbon tetracyclic lactones to which are attached two deoxysugars. Most of the genes involved in spinosyn biosynthesis are clustered in an 74 kb region of the S. spinosa genome. This region has been characterized by DNA sequence analysis and by targeted gene disruptions. The spinosyn biosynthetic gene cluster contains five large genes encoding a type I polyketide synthase, and 14 genes involved in modification of the macrolactone, or in the synthesis, modification and attachment of the deoxysugars. Four genes required for rhamnose biosynthesis (two of which are also required for forosamine biosynthesis) are not present in the cluster. A pathway for the biosynthesis of spinosyns is proposed.

Animals↗

PubMed2002

Small Cab-like proteins regulating tetrapyrrole biosynthesis in the cyanobacterium Synechocystis sp. PCC 6803.

In the cyanobacterium Synechocystis sp. PCC 6803 five open reading frames (scpA-scpE) have been identified that code for single-helix proteins resembling helices I and III of chlorophyll a/b-binding (Cab) antenna proteins from higher plants. They have been named SCPs (small Cab-like proteins). Deletion of a single scp gene in a wild-type or in a photosystem I-less (PS I-less) strain has little effect. However, the effects of functional deletion of scpB or scpE were remarkable under conditions where chlorophyll availability was limited. When cells of a strain lacking PS I and chlL (coding for a polypeptide needed for light-independent protochlorophyllide reduction) were grown in darkness, the phycobilin and protochlorophyllide levels decreased upon deletion of scpB or scpE and the protoheme level was reduced in the strain lacking scpE. Addition of delta-aminolevulinic acid (ALA) in darkness drastically increased the level of Mg-protoporphyrin IX and Mg-protoporphyrin IX monomethyl ester in the PS I-less/ch/L-/scpE- strain, whereas PChlide accumulated in the PS I-less/chlL-/scpB- strain. In the PS I-less/chlL- control strain ALA supplementation did not lead to large changes in the levels of tetrapyrrole biosynthesis intermediates. We propose that ScpE and ScpB regulate tetrapyrrole biosynthesis as a function of pigment availability. This regulation occurs primarily at an early step of tetrapyrrole biosynthesis, prior to ALA. In view of the conserved nature of chlorophyll-binding sites in these proteins, it seems likely that regulation by SCPs occurs as a function of chlorophyll availability, with SCPs activating chlorophyll biosynthesis steps when they do not have pigments bound.

Algal Proteins↗

PubMed1990

Increased thromboxane biosynthesis in childhood hemolytic uremic syndrome.

Vascular endothelial cell damage plays a central role in the pathogenesis of the hemolytic uremic syndrome (HUS), resulting in intravascular platelet activation and thrombotic microangiopathy. A deficiency of the antiaggregatory prostacyclin (PGI2) has been postulated by experiments under ex vivo conditions. However, this observation has not been confirmed in vivo. The pathophysiological contribution of thromboxane (Tx)A2, a potent vasoconstrictor and platelet-aggregating prostanoid which is predominantly produced by platelets, has not been elucidated so far. In order to quantitate endogenous formation of TxA2 in children with HUS, plasma concentrations of the enzymatic metabolite 11-dehydro-TxB2 of TxA2 and urinary excretion rates of three major TxA2 metabolites, TxB2, 11-dehydro-TxB2 and 2,3-dinor-TxB2 were analyzed using gas chromatography/mass spectrometry. PGI2 biosynthesis was assessed by measuring urinary excretion of an index metabolite of its systemic production, 2,3-dinor-6-keto-prostaglandin (PG) F1 alpha, and an index of its renal production, 6-keto-PGF1 alpha. TxA2 biosynthesis was markedly elevated in the acute phase of HUS. This activation could be detected for a longer period of time than the presence of thrombocytopenia. Concomitantly in the acute phase, renal PGI2 formation was significantly elevated and systemic PGI2 formation was elevated in 50% of the patients. These data indicate that TxA2 formation is increased in the acute phase in patients with HUS. This enhanced biosynthesis is consistent with increased platelet activation, whereas the increased PGI2 biosynthesis reflects predominantly renal endothelial cell damage.

Child↗

PubMed2025

Guanine nucleotide biosynthesis blockade impairs MLL complex formation and sensitizes leukemias to menin inhibition.

Targeting the dependency of MLL-rearranged (MLLr) leukemias on menin with small molecule inhibitors has opened new therapeutic strategies for these poor-prognosis diseases. However, the rapid development of menin inhibitor resistance calls for combinatory strategies to improve responses and prevent resistance. Here we show that leukemia stem cells (LSCs) of MLLr acute myeloid leukemia (AML) exhibit enhanced guanine nucleotide biosynthesis, the inhibition of which leads to myeloid differentiation and sensitization to menin inhibitors. Mechanistically, targeting inosine monophosphate dehydrogenase 2 (IMPDH2) reduces guanine nucleotides and rRNA transcription, leading to reduced protein expression of LEDGF and menin. Consequently, the formation and chromatin binding of the MLL-fusion complex is impaired, reducing the expression of MLL target genes. Inhibition of guanine nucleotide biosynthesis or rRNA transcription further suppresses MLLr AML when combined with a menin inhibitor. Our findings underscore the requirement of guanine nucleotide biosynthesis in maintaining the function of the LEDGF/menin/MLL-fusion complex and provide a rationale to target guanine nucleotide biosynthesis to sensitize MLLr leukemias to menin inhibitors.

Proto-Oncogene Proteins↗

PubMed2002

Light regulation of carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata.

We have studied carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata, which contains a great variety of carotenoids belonging to both the alpha- and the beta-carotene (Car) biosyntheses pathways. This unusual carotenoid composition allowed us to address the problem of how biosynthesis on the alpha- and the beta-Car pathway is regulated in response to different light regimes. We found that illumination with 4 h of actinic high light (HL, 250 micromol m(-2) s(-1)), and culture growth in permanent light (PL, 60 micromol m(-2) s(-1)). induced the de novo synthesis of violaxanthin (Vx) cycle pigments belonging to the beta-Car pathway. Carotenoid synthesis on the alpha-Car biosynthesis pathway led to a strong accumulation of lutein (L) and dihydrolutein (DhL). Both the newly synthesised Vx cycle pigments and L/DhL can be regarded as intermediate pools of carotenoids that were converted to light-harvesting pigments in low light (LL) periods following the phases of HL illumination. This transition to the light-harvesting pigments included the conversion of Vx to neoxanthin (Nx) on the beta-Car pathway, and the transformation of L/DhL to prasinoxanthin (Px), the main light-harvesting pigment of M. squamata belonging to the alpha-carotenoids. Isolation of light-harvesting complexes from L-enriched M. squamata cells showed that both L and the Vx cycle pigments were loosely bound to the LHC apoprotein. This peripheral binding is in agreement with their proposed role as intermediate pigments in the biosynthesis of light-harvesting pigments, and should allow a smooth detachment from the protein in periods of LL when the synthesis of Nx and Px is stimulated. We conclude that carotenoid synthesis proceeds in general in an economical way: in both, the alpha- and the beta-Car pathway HL induces the formation of photoprotective pigments, which in LL periods following the HL illumination are not degraded, but on the contrary are converted to light-harvesting pigments.

Carotenoids↗

PubMed2005

Biosynthesis of iso-fatty acids in myxobacteria.

The fatty acid (FA) profiles of the myxobacteria Stigmatella aurantiaca and Myxococcus xanthus were investigated by acidic methanolysis of total cell extracts and GC or GC-MS analysis. The main components were 13-methyltetradecanoic acid (iso-15:0) and (Z)-hexadec-11-enoic acid (16:1, omega-5 cis). The biosynthesis of iso-FAs was investigated in several feeding experiments. Feeding of isovaleric acid (IVA) to a mutant impaired in the degradation of leucine to isovaleryl-CoA (IV-CoA)(bkd mutant) of M. xanthus only increased the amount of iso-odd FAs, whereas feeding of isobutyric acid (IBA) gave increased amounts only of iso-even FAs. In contrast, a bkd mutant of S. aurantiaca gave increased amounts of iso-odd and iso-even fatty acids in both experiments. We assumed that in S. aurantiacaalpha-oxidation takes place. [D(7)]-15-Methylhexadecanoic acid was synthesised and fed to S. aurantiaca as well as [D(10)]leucine and [D(8)]valine to elucidate this pathway in more detail. The iso-fatty acid was degraded by alpha- and beta-oxidation steps. [D(10)]Leucine was strongly incorporated into iso-odd and iso-even fatty acids, whereas the incorporation rates for [D(8)]valine into both types of fatty acids were low. Thus alpha-oxidation plays an important role in the biosynthesis of iso-fatty acids in S. aurantiaca. The incorporation rates observed after feeding of [D(10)]leucine and [D(8)]valine are the highest for iso-17:0 compared to the other acids. This indicates the central role of iso-17:0 in the biosynthesis of iso-FAs. The shorter homologues seem to be formed mainly by alpha-oxidation and beta-oxidation of this acid. After feeding of traces of unsaturated counterparts of this labelled FA occurred in the extracts indicating that desaturases are active in the biosynthesis of unsaturated fatty acids in S. aurantiaca.

Chromatography, Thin Layer↗