Subcellular localization of two long-chain acyl-coenzyme-A synthetases in Candida lipolytica

Production of lactones for flavoring and pharmacological purposes from unsaturated lipids: an industrial perspective

The enantiomeric pure and natural (+)-Lactones (C ≤ 14) with aromas obtained from fruits and milk are considered flavoring compounds. The flavoring value is related to the lactones' ring size and chain length, which blend in varying concentrations to produce different stone-fruit flavors. The nature-identical and enantiomeric pure (+)-lactones are only produced through whole-cell biotransformation of yeast. The industrially important γ-decalactone and δ-decalactone are produced by a four-step aerobic-oxidation of ricinoleic acid (RA) following the lactonization mechanism. Recently, metabolic engineering strategies have opened up new possibilities for increasing productivity. Another strategy for increasing yield is to immobilize the RA and remove lactones from the broth regularly. Besides flavor impact, γ-, δ-, ε-, ω-lactones of the carbon chain (C8-C12), the macro-lactones and their derivatives are vital in pharmaceuticals and healthcare. These analogues are isolated from natural sources or commercially produced via biotransformation and chemical synthesis processes for medicinal use or as active pharmaceutical ingredients. The various approaches to biotransformation have been discussed in this review to generate more prospects from a commercial point of view. Finally, this work will be regarded as a magical brick capable of containing both traditional and genetic engineering technology while contributing to a wide range of commercial applications.

A Vectorial, ER-Mitochondria Link to Energy Homeostasis in the Vascular Endothelium

The precise mechanisms of free fatty acid (FFA) uptake in the vascular endothelium are unclear. In this issue of Cell Metabolism, Ibrahim et al. (2020) discover that FFA uptake is partially mediated by a vectorial, ER-mitochondria link, in which mitochondrial ATP production is locally used for the acyl-CoA synthetase activity of the ER-located fatty acid transport protein 4.

Peroxisomal acyl-CoA synthetases

Peroxisomes carry out many essential lipid metabolic functions. Nearly all of these functions require that an acyl group-either a fatty acid or the acyl side chain of a steroid derivative-be thioesterified to coenzyme A (CoA) for subsequent reactions to proceed. This thioesterification, or "activation", reaction, catalyzed by enzymes belonging to the acyl-CoA synthetase family, is thus central to cellular lipid metabolism. However, despite our rather thorough understanding of peroxisomal metabolic pathways, surprisingly little is known about the specific peroxisomal acyl-CoA synthetases that participate in these pathways. Of the 26 acyl-CoA synthetases encoded by the human and mouse genomes, only a few have been reported to be peroxisomal, including ACSL4, SLC27A2, and SLC27A4. In this review, we briefly describe the primary peroxisomal lipid metabolic pathways in which fatty acyl-CoAs participate. Then, we examine the evidence for presence and functions of acyl-CoA synthetases in peroxisomes, much of which was obtained before the existence of multiple acyl-CoA synthetase isoenzymes was known. Finally, we discuss the role(s) of peroxisome-specific acyl-CoA synthetase isoforms in lipid metabolism.

Bioinformatic Analysis of Leishmania donovani Long-Chain Fatty Acid-CoA Ligase as a Novel Drug Target

Fatty acyl-CoA synthetase (fatty acid: CoA ligase, AMP-forming; (EC 6.2.1.3)) catalyzes the formation of fatty acyl-CoA by a two-step process that proceeds through the hydrolysis of pyrophosphate. Fatty acyl-CoA represents bioactive compounds that are involved in protein transport, enzyme activation, protein acylation, cell signaling, and transcriptional control in addition to serving as substrates for beta oxidation and phospholipid biosynthesis. Fatty acyl-CoA synthetase occupies a pivotal role in cellular homeostasis, particularly in lipid metabolism. Our interest in fatty acyl-CoA synthetase stems from the identification of this enzyme, long-chain fatty acyl-CoA ligase (LCFA) by microarray analysis. We found this enzyme to be differentially expressed by Leishmania donovani amastigotes resistant to antimonial treatment. In the present study, we confirm the presence of long-chain fatty acyl-CoA ligase gene in the genome of clinical isolates of Leishmania donovani collected from the disease endemic area in India. We predict a molecular model for this enzyme for in silico docking studies using chemical library available in our institute. On the basis of the data presented in this work, we propose that long-chain fatty acyl-CoA ligase enzyme serves as an important protein and a potential target candidate for development of selective inhibitors against leishmaniasis.

Unique glycerophospholipid signature in retinal stem cells correlates with enzymatic functions of diverse long-chain acyl-CoA synthetases

Lipidomics is an emerging research field that comprehensively characterizes lipid molecular species and their metabolic regulation and biological roles. We performed the first lipidomics study on glycerophospholipids (GPLs) in adult mammalian retinal stem cells (RSCs) and non-RSC control cells. A unique GPL signature identified by electrospray ionization tandem mass spectrometry showed new prominent peaks of 16:0 (sn-1)-18:0 (sn-2) or 16:0-16:0 saturated fatty acids, instead of 18:0-20:4 or 18:0-22:6 polyunsaturated essential fatty acids, at 720 m/z of phosphatidylethanolamine, 764 m/z of phosphatidylserine, and 809 m/z of phosphatidylinositol in RSCs (sphere colony RSCs and enriched RSCs), but not in non-RSCs (retinal cells, ciliary cells, sphere colony-derived retinal cells, and nonretinal cells). To seek whether the GPL signature was associated with long-chain acyl-CoA synthetase (LACS), a potential modulator of fatty acid profiles in de novo GPL synthesis, we analyzed gene expression, catabolic activity, substrate selectivity, and inhibitor sensitivity of diverse LACSs. LACSs in RSCs mediated less utilization by GPLs of polyunsaturated essential fatty acids, including arachidonic acid (20:4 [n-6], a second messenger in cell signaling), which was accompanied by lower plasma membrane fluidity in proliferating RSCs compared with differentiated non-RSCs. These novel findings suggest that LACS-associated GPL signature and cell membrane fluidity may participate in regulating proliferation versus differentiation in RSCs and, perhaps, other types of stem cells.

Hydrophobic substrate utilisation by the yeast , and its potential applications

The alkane-assimilating yeast Yarrowia lipolytica degrades very efficiently hydrophobic substrates such as n-alkanes, fatty acids, fats and oils for which it has specific metabolic pathways. An overview of the oxidative degradation pathways for alkanes and triglycerides in Y. lipolytica is given, with new insights arising from the recent genome sequencing of this yeast. This includes the interaction of hydrophobic substrates with yeast cells, their uptake and transport, the primary alkane oxidation to the corresponding fatty alcohols and then by different enzymes to fatty acids, and the subsequent degradation in peroxisomal beta-oxidation or storage into lipid bodies. Several enzymes involved in hydrophobic substrate utilisation belong to multigene families, such as lipases/esterases (LIP genes), cytochromes P450 (ALK genes) and peroxisomal acyl-CoA oxidases (POX genes). Examples are presented demonstrating that wild-type and genetically engineered strains of Y. lipolytica can be used for alkane and fatty-acid bioconversion, such as aroma production, for production of SCP and SCO, for citric acid production, in bioremediation, in fine chemistry, for steroid biotransformation, and in food industry. These examples demonstrate distinct advantages of Y. lipolytica for their use in bioconversion reactions of biotechnologically interesting hydrophobic substrates.

Structural basis of the substrate-specific two-step catalysis of long chain fatty acyl-CoA synthetase dimer

Long chain fatty acyl-CoA synthetases are responsible for fatty acid degradation as well as physiological regulation of cellular functions via the production of long chain fatty acyl-CoA esters. We report the first crystal structures of long chain fatty acyl-CoA synthetase homodimer (LC-FACS) from Thermus thermophilus HB8 (ttLC-FACS), including complexes with the ATP analogue adenosine 5'-(beta,gamma-imido) triphosphate (AMP-PNP) and myristoyl-AMP. ttLC-FACS is a member of the adenylate forming enzyme superfamily that catalyzes the ATP-dependent acylation of fatty acid in a two-step reaction. The first reaction step was shown to propagate in AMP-PNP complex crystals soaked with myristate solution. Myristoyl-AMP was identified as the intermediate. The AMP-PNP and the myristoyl-AMP complex structures show an identical closed conformation of the small C-terminal domains, whereas the uncomplexed form shows a variety of open conformations. Upon ATP binding, the fatty acid-binding tunnel gated by an aromatic residue opens to the ATP-binding site. The gated fatty acid-binding tunnel appears only to allow one-way movement of the fatty acid during overall catalysis. The protein incorporates a hydrophobic branch from the fatty acid-binding tunnel that is responsible for substrate specificity. Based on these high resolution crystal structures, we propose a unidirectional Bi Uni Uni Bi Ping-Pong mechanism for the two-step acylation by ttLC-FACS.

Evaluation of acyl coenzyme A oxidase (Aox) isozyme function in the n-alkane-assimilating yeast Yarrowia lipolytica

We have identified five acyl coenzyme A (CoA) oxidase isozymes (Aox1 through Aox5) in the n-alkane-assimilating yeast Yarrowia lipolytica, encoded by the POX1 through POX5 genes. The physiological function of these oxidases has been investigated by gene disruption. Single, double, triple, and quadruple disruptants were constructed. Global Aox activity was determined as a function of time after induction and of substrate chain length. Single null mutations did not affect growth but affected the chain length preference of acyl-CoA oxidase activity, as evidenced by a chain length specificity for Aox2 and Aox3. Aox2 was shown to be a long-chain acyl-CoA oxidase and Aox3 was found to be active against short-chain fatty acids, whereas Aox5 was active against molecules of all chain lengths. Mutations in Aox4 and Aox5 resulted in an increase in total Aox activity. The growth of mutant strains was analyzed. In the presence of POX1 only, strains did not grow on fatty acids, whereas POX4 alone elicited partial growth, and the growth of the double POX2-POX3-deleted mutant was normal excepted on plates containing oleic acid as the carbon source. The amounts of Aox protein detected by Western blotting paralleled the Aox activity levels, demonstrating the regulation of Aox in cells according to the POX genotype.

Selective peroxisome degradation in Yarrowia lipolytica after a shift of cells from acetate/oleate/ethylamine into glucose/ammonium sulfate-containing media

We have shown that peroxisomes of the yeast Yarrowia lipolytica are subject to specific degradation after exposure of acetate/oleate-grown cells to glucose excess conditions. Electron microscopic analysis has revealed that the peroxisomes were degraded by uptake in the vacuole. Our results suggest that peroxisomes are taken up by macroautophagic processes, because sequestration of individual peroxisomes, which occurs typically at the beginning of microautophagy, was never observed. The observation that a peroxisomal amine oxidase activity is specifically induced by ethylamine was used for the development of a plate assay screening procedure to isolate peroxisome degradation-defective mutants.

In vivo regulation of acyl-CoA synthetase mRNA and activity by endotoxin and cytokines

Acyl-CoA synthetase (ACS) catalyzes the activation of fatty acids (FA) to acyl-CoA esters, which are further metabolized in either anabolic or catabolic pathways. Endotoxin [lipopolysaccharide (LPS)], tumor necrosis factor (TNF), and interleukin-1 (IL-1) enhance hepatic FA synthesis and reesterification and inhibit FA oxidation. LPS also decreases triglyceride storage in adipose tissue and inhibits the uptake of FA by heart and muscle. Therefore, in this study we examined the effects of LPS and cytokines on ACS (now also known as ACS1) mRNA expression and activity in multiple tissues in Syrian hamsters. LPS markedly decreased ACS1 mRNA levels in liver, adipose tissue, heart, and skeletal muscle. The inhibitory effects of LPS on ACS1 mRNA levels in liver and adipose tissue were observed as early as 2-4 h after administration, became maximal by 4-8 h, and were sustained for >/=24 h. Very low doses of LPS (0.1-1 microg/100 g body wt) were needed to reduce ACS1 mRNA levels in liver and adipose tissue. TNF and IL-1 mimicked the effect of LPS on ACS1 mRNA levels in liver and adipose tissue. LPS decreased ACS activity in adipose tissue, heart, and muscle. In liver, where ACS is localized in several subcellular organelles, both LPS and cytokines decreased mitochondrial ACS activity, whereas they increased microsomal ACS activity. Taken together, these results indicate that LPS and cytokines decrease ACS1 mRNA expression and ACS activity in tissues where FA uptake and/or oxidation is decreased during sepsis. In liver, where FA oxidation is decreased during sepsis but the reesterification of FA is increased, LPS and cytokines decrease ACS1 mRNA and mitochondrial ACS activity, which may inhibit FA oxidation, but increase microsomal ACS activity, which may support the reesterification of peripherally derived FA for triglyceride synthesis.

Two distinct long-chain-acyl-CoA synthetases in guinea pig Harderian gland

Two distinct long-chain-acyl-CoA synthetases which have different kinetic properties were identified in the guinea pig Harderian gland. One was localized in the microsomes and the other in the mitochondria. The relative V(max) values of the microsomal enzyme were 8.1, 1.7 and 1 and the apparent Km values were 66.7, 12.0 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values of the mitochondrial enzyme were 2.7, 3.5 and 1 and the apparent Km values were 33.3, 29.9 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values for the liver microsomal enzyme were 2.0, 2.5 and 1, while those of the liver mitochondrial enzyme were 4.1, 3.9 and 1 with palmitic, linoleic and arachidonic acids, respectively. There were no difference between the microsomal and the mitochondrial enzymes in the liver, regarding apparent Km values; these were 38.4, 29.9 and 22.0 microM for palmitic, linoleic and arachidonic acids, respectively. Thus, the substrate specificity and catalytic rate of the mitochondrial enzyme in Harderian gland for palmitic, linoleic and arachidonic acids were similar to the liver enzyme, but not to the microsomal enzyme in Harderian gland. On the other hand, the antiserum raised against the rat liver enzyme immune-titrated and immuno-blotted the enzymes from Harderian gland microsomes and liver, but not so the enzyme from Harderian gland mitochondria. Thus, the microsomal enzyme in Harderian gland had a common immunogenic epitope(s) with the liver enzyme, but the mitochondrial enzyme did not. The Harderian gland mitochondrial enzyme was a distinct protein from liver enzymes. The catalytic and immunogenic characteristics suggest that the enzyme proteins in the Harderian gland are unique, that is, different from that in the liver. The large V(max) value of the Harderian gland microsomal enzyme for palmitic acid suggests that it contributes to the synthesis of a large amount of the secretory lipid and the high Km value to maintenance of cellular lipid in this organ. The evidence that long-chain-acyl-CoA synthetase in the mitochondria is distinct from that in the microsomes was first found in guinea pig Harderian gland.

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

Multiple promoters in rat acyl-CoA synthetase gene mediate differential expression of multiple transcripts with 5'-end heterogeneity

Nucleotide sequence analysis of six independently isolated cDNAs for rat acyl-CoA synthetase (ACS) revealed three forms of ACS mRNA, designated form-A, -B, and -C mRNAs, which differ in their 5'-untranslated regions. Form-A mRNA was preferentially detected in normal and peroxisome-induced livers, whereas form-B mRNA was found in peroxisome-induced livers but not in normal livers and hearts, and form-C mRNA was preferentially found in normal hearts and peroxisome-induced livers. Analysis of two overlapping genomic clones for the rat ACS gene revealed that the three 5'-untranslated regions of the mRNAs are individually encoded by three different exons located within a 20-kilobase genomic fragment. The transcription start sites of the three forms of ACS mRNA were determined and nucleotide sequences of 5'-upstream regions of the three 5'-end exons were determined. The 5'-upstream regions were fused to the chloramphenicol acetyltransferase gene and transcription units of the three forms of ACS mRNAs were determined. These data indicate that the three forms of ACS mRNA with 5'-end heterogeneity are generated by alternative transcription from three promoters in the rat ACS gene.

Isolation of a Saccharomyces cerevisiae long chain fatty acyl:CoA synthetase gene (FAA1) and assessment of its role in protein N-myristoylation

Regulation of myristoylCoA pools in Saccharomyces cerevisiae plays an important role in modulating the activity of myristoylCoA:protein N-myristoyltransferase (NMT), an essential enzyme with an ordered Bi Bi reaction that catalyzes the transfer of myristate from myristoylCoA to greater than or equal to 12 cellular proteins. At least two pathways are available for generating myristoylCoA: de novo synthesis by the multifunctional, multisubunit fatty acid synthetase complex (FAS) and activation of exogenous myristate by acylCoA synthetase. The FAA1 (fatty acid activation) gene has been isolated by genetic complementation of a faal mutant. This single copy gene, which maps to the right arm of chromosome XV, specifies a long chain acylCoA synthetase of 700 amino acids. Analyses of strains containing NMT1 and a faal null mutation indicated that FAA1 is not essential for vegetative growth when an active de novo pathway for fatty acid synthesis is present. The role of FAA1 in cellular lipid metabolism and protein N-myristoylation was therefore assessed in strains subjected to biochemical or genetic blockade of FAS. At 36 degrees C, FAA1 is required for the utilization of exogenous myristate by NMT and for the synthesis of several phospholipid species. This requirement is not apparent at 24 or 30 degrees C, suggesting that S. cerevisiae contains another acylCoA synthetase activity whose chain length and/or temperature optima may differ from Faalp.

Two acyl-coenzyme A oxidases in peroxisomes of the yeast Candida tropicalis: primary structures deduced from genomic DNA sequence

We report the complete nucleotide sequence of two genes encoding major peroxisomal polypeptides (PXPs) of Candida tropicalis. One, POX4, encodes PXP-4, which is the most abundant polypeptide in cells grown on oleic acid, and the other, POX5, is the gene for PXP-5. Each of the two polypeptides was found to be the subunit of a distinct long-chain acyl-coenzyme A oxidase: acyl-CoA oxidase II (PXP-4) or acyl-CoA oxidase I (PXP-5). Both the genes had no intron and gave a single open reading frame. The NH2-terminal sequences, except the initiator methionine, and the calculated molecular weights of the deduced polypeptides were consistent with those of the respective PXPs. Well-conserved sequences of 12 and 16 hydrophobic amino acids were present in the middle of the polypeptide, instead of at the NH2 terminus, and may be internal signal sequences for the peroxisomal location of PXPs. Although the two polypeptides were significantly homologous throughout their sequences, the local homologies in two regions out of five were markedly diverged from the average (63%); the homology in the second region was 93%, whereas that in the fourth one was only 24%. The implications of this finding are discussed in respect to the multiplicity of peroxisomal enzymes and the presence of multifunctional proteins in peroxisomes.

High-level expression and molecular cloning of genes encoding Candida tropicalis peroxisomal proteins

The development of peroxisomes in the cells of Candida tropicalis grown on oleic acid was accompanied by a markedly high expression of peroxisomal proteins. On the basis of this finding, the nuclear DNA library of this yeast was screened by differential hybridization, and 102 clones of oleic acid-inducible sequences were isolated. Seven coding regions were found to form clusters in three stretches of the genomic DNA. Five of the regions were identified as genes for peroxisomal polypeptides (PXPs). The coding sequence for PXP-2 hybrid selected an additional mRNA for PXP-4, the subunit of long-chain acyl coenzyme A oxidase, which was the most abundant PXP. PXP-2 and PXP-4 were close in apparent molecular weight and generated similar peptides when digested with a protease. The gene for PXP-4 was adjacent to that for PXP-2 on the genome and also hybridized to the mRNA coding for PXP-5. These and other similar results suggest that the genes for the peroxisomal proteins of this organism arose by duplication of a few ancestral genes.

High-level expression and molecular cloning of genes encoding Candida tropicalis peroxisomal proteins

The development of peroxisomes in the cells of Candida tropicalis grown on oleic acid was accompanied by a markedly high expression of peroxisomal proteins. On the basis of this finding, the nuclear DNA library of this yeast was screened by differential hybridization, and 102 clones of oleic acid-inducible sequences were isolated. Seven coding regions were found to form clusters in three stretches of the genomic DNA. Five of the regions were identified as genes for peroxisomal polypeptides (PXPs). The coding sequence for PXP-2 hybrid selected an additional mRNA for PXP-4, the subunit of long-chain acyl coenzyme A oxidase, which was the most abundant PXP. PXP-2 and PXP-4 were close in apparent molecular weight and generated similar peptides when digested with a protease. The gene for PXP-4 was adjacent to that for PXP-2 on the genome and also hybridized to the mRNA coding for PXP-5. These and other similar results suggest that the genes for the peroxisomal proteins of this organism arose by duplication of a few ancestral genes.

Induction and subcellular localization of enzymes participating in propionate metabolism in Candida tropicalis

Candida tropicalis, a representative alkane- and higher fatty acid-utilizing yeast, can grow on propionate used as sole carbon and energy source. Initial pH of the medium markedly affected the growth of the yeast on propionate. In propionate-grown cells, several enzymes associated with peroxisomes and/or participating in propionate metabolism were induced in connection with the appearance of the characteristic peroxisomes. Acetate-grown cells of this yeast had only few peroxisomes, while alkane-grown cells contained conspicuous numbers of the organelles. As compared with alkane-grown cells, some specific features were observed in peroxisomes and enzymes associated with the organelles of propionate-grown cells: The shape of peroxisomes was large but the number was small; unlike localization of catalase in peroxisomes of alkane-grown cells, the enzyme of propionate-grown cells was mainly localized in cytoplasm; as for carnitine acetyltransferase localized almost equally in peroxisomes and mitochondria in alkane-grown cells, propionate-grown cells contained mainly the mitochondrial type enzyme. A propionate-activating enzyme, which was different from acetyl-CoA synthetase, was also induced in cytoplasm of propionate-grown cells. The role of carnitine acetyltransferase and the propionate-activating enzyme in propionate metabolism is discussed in comparison with the role of carnitine acetyltransferase and acetyl-CoA synthetase in acetate metabolism.

Control of triglyceride synthesis by the intracellular level of long-chain acyl coenzyme A for lipid synthesis

Candida lipolytica mutants defective in acyl coenzyme A synthetase I synthesized triglyceride to a markedly less extent than did the wild-type yeast, when grown on oleic acid. The synthesis of triglyceride was controlled by the level of long-chain acyl coenzyme A available for lipid synthesis, whereas the synthesis of phospholipids was hardly affected.

Chemical and catalytic properties of the peroxisomal acyl-coenzyme A oxidase from Candida tropicalis

The peroxisomal acyl-CoA oxidase has been purified from extracts of the yeast Candida tropicalis grown with alkanes as the principal energy source. The enzyme has a molecular weight of 552,000 and a subunit molecular weight of 72,100. Using an experimentally determined molar extinction coefficient for the enzyme-bound flavin, a minimum molecular weight of 146,700 was determined. Based on these data, the oxidase contains eight perhaps identical subunits and four equivalents of FAD. No other beta-oxidation enzyme activities are detected in purified preparations of the oxidase. The oxidase flavin does not react with sulfite to form an N(5) flavin-sulfite complex. Photochemical reduction of the oxidase flavin yields a red semiquinone; however, the yield of semiquinone is strongly pH dependent. The yield of semiquinone is significantly reduced below pH 7.5. The flavin semiquinone can be further reduced to the hydroquinone. The behavior of the oxidase flavin during photoreduction and its reactivity toward sulfite are interpreted to reflect the interaction in the N(1)-C(2)O region of the flavin with a group on the protein which acts as a hydrogen-bond acceptor. Like the acyl-CoA dehydrogenases which catalyze the same transformation of acyl-CoA substrates, the oxidase is inactivated by the acetylenic substrate analog, 3-octynoyl-CoA, which acts as an active site-directed inhibitor.

Absence of DNA in peroxisomes of Candida tropicalis

Yeast peroxisomes were purified to near homogeneity from cells of Candida tropicalis grown on oleic acid for the purpose of examining the possible presence of DNA in this organelle. The purification procedure includes the effective conversion of cells to spheroplasts with Zymolyase and sodium sulfite and the separation of the organelles at extremely low ionic strength. The mitochondrial contamination was less than 1%, based on several criteria, and the yield of peroxisomes was about 40%. The purified peroxisomal fraction contained a very small amount of DNA, which yielded restriction fragments indistinguishable from those of mitochondrial DNA. The absence of DNA in peroxisomes was also supported by cesium chloride density gradient centrifugation of the organelles lysed with a detergent, staining of the organelles with a fluorescent dye specific to DNA, and labeling of the DNA with [3H]adenine.

Subcellular localization of the methylcitric-acid-cycle enzymes in propionate metabolism of Yarrowia lipolytica

The subcellular localization of the four characteristic enzymes of the methylcitric acid cycle was studied with glucose-grown as well as n-alkane-grown cells of Yarrowia lipolytica. Microsomes and peroxisomes showed no cycle enzyme activities. The four cycle enzymes were constitutively localized in mitochondria, with the exception of the dual localization of the fourth enzyme, 2-methylisocitrate lyase, in mitochondria and cytoplasm, where the lyase may function to supply pyruvate (the end-product of the catabolism of the propionate residue) to various reactions.

Peroxisomal and mitochondrial carnitine acetyltransferases in alkane-grown yeast Candida tropicalis

Two types of carnitine acetyltransferases (EC 2.3.1.7) were first isolated from a microorganism, alkane-grown yeast Candida tropicalis. Carnitine acetyltransferase activity was induced in the alkane-grown cells, reaching about twenty times higher than that in the glucose-grown cells. Localization of the enzyme activity was demonstrated, at least, in peroxisomes (microbodies), profusely occurred in the alkane-grown cells, and in mitochondria. Peroxisomal and mitochondrial carnitine acetyltransferases could be separated using the method of DEAE-Sephacel column chromatography and both types were found to exist in the alkane-grown cells of C. tropicalis. Each carnitine acetyltransferase was purified using Sephadex G-200, Sepharose 6B, DEAE-Sephacel and Blue-Sepharose CL-6B. In DEAE-Sephacel chromatography, peroxisomal carnitine acetyltransferase was eluted below 0.15 M KCl concentration and mitochondrial carnitine acetyltransferase above 0.15 M KCl concentration. Except for the localization, little difference was observed in their kinetic properties, substrate specificity and so on. These two carnitine acetyltransferase preparations were only specific to acetyl and propionyl groups, the substrate specificity not being so broad as that of carnitine acetyltransferase obtained from mammalian tissues. Roles of these carnitine acetyltransferases in alkane metabolism in yeast are also discussed.

Enzyme activities during early ascosporulation in Saccharomyces cerevisiae

1. Several enzyme activities were examined during the initial sporulating phase in Saccharomyces cerevisiae. 2. Catalase activity increased obviously after transfer to sporulation medium. 3. Catalase is probably considered to play an essential role in sporulation. 4. Both activities of inorganic pyrophosphatase and glycerol-2-phosphatase decreased. 5. Conditions necessary for sporulation were suggested.

Subcellular localization of long-chain alcohol dehydrogenase and aldehyde dehydrogenase in n-alkane-grown Candida tropicalis

Long-chain alcohol dehydrogenase and long-chain aldehyde dehydrogenase were induced in the cells of Candida tropicalis grown on n-alkanes. Subcellular localization of these dehydrogenases, together with that of acyl-CoA synthetase and glycerol-3-phosphate acyltransferase, was studied in terms of the metabolism of fatty acids derived from n-alkane substrates. Both long-chain alcohol and aldehyde dehydrogenases distributed in the fractions of microsomes, mitochondria and peroxisomes obtained from the alkane-grown cells of C. tropicalis. Acyl-CoA synthetase was also located in these three fractions. Glycerol-3-phosphate acyltransferase was found in microsomes and mitochondria, in contrast to fatty acid beta-oxidation system localized exclusively in peroxisomes. Similar results of the enzyme localization were also obtained with C. lipolytica grown on n-alkanes. These results suggest strongly that microsomal and mitochondrial dehydrogenases provide long-chain fatty acids to be utilized for lipid synthesis, whereas those in peroxisomes supply fatty acids to be degraded via beta-oxidation to yield energy and cell constituents.

Effects of fat content in the diet on hepatic peroxisomes of the rat

Effects of fat content in the diet on rat liver peroxisomes was examined. In the livers of rats fed for one week on the high-fat diet containing 30% fat, the cyanide-insensitive palmitoyl-CoA oxidation was accelerated to eight times that of control and the enzymic activities of catalase, carnitine acetyltransferase and carnitine palmitoyltransferase were elevated by the factors of 1.3, 5 and 2, respectively. In contrast, the activities of D-amino acid oxidase in addition to the three enzymes mentioned above were all lowered by 20% when the animals were maintained on a fat-free diet for the same period of time. It appears that the high-fat diet-induced increase in the activity of carnitine palmitoyltransferase is a result of the raised activity of this enzyme in mitochondria only while the apparent high activity reflects stimulation of carnitine acetyltransferase in all the subcellular fractions. Another notable effect of the high-fat diet was a remarkable increase in the quantity of a peroxisome-associated polypeptide which was separable by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It is noteworthy that this effect of the high-fat diet resemble that of clofibrate. If the diet was deprived of fat, however, this polypeptide species, with an estimated molecular weight of 80 000, decreased to a level slightly lower than normal. On the basis of the electron micrographic criteria, the high-fat diet provoked a marked proliferation of hepatic peroxisomes.

Acyl-coenzyme-A synthetase I from Candida lipolytica. Purification, properties and immunochemical studies

Acyl-coenzyme-A synthetase I from Candida lipolytica has been purified to homogeneity as evidenced by polyacrylamide gel electrophoresis in the presence and absence of dodecylsulfate as well as by Ouchterlony double-diffusion analysis. The purification procedure involves resolution of cellular particles with Triton X-100 and chromatography on phosphocellulose, Blue-Sepharose and Sephadex G-100. The purified enzyme exhibits a specific activity of 20--24 U/mg protein at 25 degree C, which is about 100-fold higher than those of long-chain acyl-CoA synthetases hitherto reported. The molecular weight of the enzyme has been estimated by polyacrylamide gel electrophoresis in the presence of dodecylsulfate to be approximately 84 000. The enzyme is specific for fatty acids with 14--18 carbon atoms regardless of the degree of unsaturation. Studies with the use of specific antibody to acyl-CoA synthetase I have indicated that this enzyme is immunochemically distinguishable from acyl-CoA synthetase II.