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PubMed1989

delta-Aminolevulinic acid biosynthesis in Escherichia coli and Bacillus subtilis involves formation of glutamyl-tRNA.

Cell-free extracts of Escherichia coli and Bacillus subtilis catalyzed the tRNA-dependent, RNase A-sensitive formation of delta-aminolevulinic acid (ALA) from glutamate. Cell extracts prepared from cultures of E. coli grown under aerobic or anaerobic conditions had similar levels of ALA biosynthetic activity. Both the tRNA-stimulated conversion of glutamate to ALA and the conversion of glutamate-1-semialdehyde to ALA were inhibited by gabaculin. However, gabaculin had no effect on the growth of either E. coli or B. subtilis. The tRNA-dependent transformation of glutamate to ALA in E. coli and B. subtilis thus appears to be very similar to the pathway found in cyanobacteria, certain obligate anaerobic eubacteria, archaebacteria and in the chloroplasts of algae and higher plant species.

Alanine↗

PubMed2005

Tobacco Mg protoporphyrin IX methyltransferase is involved in inverse activation of Mg porphyrin and protoheme synthesis.

Protoporphyrin, a metabolic intermediate of tetrapyrrole biosynthesis, is metabolized by Mg chelatase and ferrochelatase and is directed into the Mg-branch for chlorophyll synthesis and in the Fe-branch for protoheme synthesis respectively. Regulation of the enzyme activities at the beginning of this branchpoint ensures accurate partition of protoporphyrin, but is still not entirely understood. Transgenic tobacco plants were generated that express antisense or sense RNA for inhibited and excessive expression of Mg protoporphyrin methyltransferase (MgPMT) respectively. This enzyme accepts Mg protoporphyrin from Mg chelatase and catalyses the transfer of a methyl group to the carboxyl group of the C13-propionate side chain. Low MgPMT activity is correlated with reduced Mg chelatase activity and a low synthesis rate of 5-aminolevulinate, but with enhanced ferrochelatase activity. In contrast, high MgPMT activity leads to inverse activity profiles: high activities of Mg chelatase and for 5-aminolevulinate synthesis, but reduced activity of ferrochelatase, indicating a direct influence of MgPMT in combination with Mg chelatase on the metabolic flux of ALA and the distribution of protoporphyrin into the branched pathway. The modified enzyme activities in tetrapyrrole biosynthesis in the transgenic plants can be explained with changes of certain corresponding mRNA contents: increased 5-aminolevulinate synthesis and Mg chelatase activity correlate with enhanced transcript levels of the HemA, Gsa, and CHLH gene encoding glutamyl-tRNA reductase, glutamate-1-semialdehyde aminotransferase and a Mg chelatase subunit respectively. It is proposed that reduced and increased MgPMT activity in chloroplasts is communicated to the cytoplasm for modulating transcriptional activities of regulatory enzymes of the pathway.

Chlorophyll↗

PubMed1984

Halobacterium volcanii tRNAs. Identification of 41 tRNAs covering all amino acids, and the sequences of 33 class I tRNAs.

Transfer RNAs of Halobacterium volcanii, an archaebacterium, were separated by two-dimensional gel electrophoresis and sequenced by a combination of methods. A total of 41 tRNAs, at least one for each amino acid, were identified. These are five tRNAs for Leu, four for Gly, three each for Ala, Arg, Pro, and Ser, two each for Glu, Ile, Lys, Met (initiator and noninitiator), Thr, and Val, and one each for the remaining eight amino acids. As in eucaryotes, only Leu and Ser tRNAs are class II (large extra arm). The sequences of the 33 class I tRNAs, for the remaining 18 amino acids, are presented here. These cover at least 44 codons out of a possible 49 codons for the 18 amino acids. Although these archaebacterial tRNAs follow general tRNA patterns, they are in detail distinct from both eucaryotic and eubacterial tRNAs. Moreover, the initiator tRNA is unique in having a 5'-triphosphorylated end.

Amino Acids↗

PubMed1994

A new gene encoding tRNA(Pro) (GGG) is present in the chloroplast genome of black pine: a compilation of 32 tRNA genes from black pine chloroplasts.

The chloroplast genome of black pine (Pinus thunbergii), a gymnosperm, contains 32 different tRNA genes, 30 of which correspond to those previously identified in tobacco and rice chloroplast genomes. Two additional genes encode tRNA(Pro) (GGG) and tRNA(Arg) (CCG); the former is newly identified while the latter is present in liverwort, Physcomitrella patens and Angiopteris lygodiifolia, chloroplast genomes. Moreover, a partial copy of the split tRNA(Gly) (UCC) gene and full copies of tRNA(His) (GUG), tRNA(Thr) (GGU) and tRNA(Ser) (GCU) genes are present in the large single-copy region of the genome, suggesting extensive rearrangements of the chloroplast genome during evolution. No tRNA genes whose tRNA products can recognize codons CUU/C (Leu) and GCU/C (Ala) have been found. We propose that the 32 tRNAs are sufficient to read all the 61 sense codons in the black pine system using the "two-out-of-three" and the "U:N wobble" mechanisms.

Base Sequence↗

PubMed1988

The tRNA Required for in Vitro delta-Aminolevulinic Acid Formation from Glutamate in Synechocystis Extracts : Determination of Activity in a Synechocystis in Vitro Protein Synthesizing System.

RNA is an essential component for the enzymic conversion of glutamate to delta-aminolevulinic acid (ALA), the universal heme and chlorophyll precursor, as carried out in plants, algae, and some bacteria. The RNA required in this process was reported to bear a close structural resemblance to tRNA(Glu(UUC)), and it can be isolated by affinity chromatography directed against the UUC anticodon. Affinity-purified tRNA(Glu(UUC)) from the cyanobacterium Synechocystis sp. PCC 6803 was resolved into two major subfractions by reverse-phase HPLC. Only one of these was effectively charged with glutamate in enzyme extract from Synechocystis, but both were charged in Chlorella vulgaris enzyme extract. When charged with glutamate, the two glutamyl-tRNA(Glu(UUC)) species produced were equally effective in supporting both ALA formation and protein synthesis in vitro, as measured by label transfer from [(3)H]glutamyl-tRNA to ALA and protein. These results indicate that one of the two tRNA(Glu(UUC)) species is used by Synechocystis for both protein biosynthesis and ALA formation. Both of the tRNA(Glu(UUC)) subfractions from Synechocystis supported ALA formation in Chlorella enzyme extract. Escherichia coli tRNA(Glu(UUC)) was charged with glutamate, but did not support ALA formation in Synechocystis enzyme extract. Unfractionated tRNA from Chlorella, pea, and E. coli, having been charged with [(3)H] glutamate by Chlorella enzyme extract and then re-isolated, were all able to transfer label to proteins in the Synechocystis enzyme extract.

Journal Article↗

PubMed2000

Hydrolytic editing by a class II aminoacyl-tRNA synthetase.

Editing reactions catalyzed by aminoacyl-tRNA synthetases are critical for accurate translation of the genetic code. To date, this activity, whereby misactivated amino acids are hydrolyzed either before or after transfer to noncognate tRNAs, has been characterized extensively only in the case of class I synthetases. Class II synthetases have an active-site architecture that is completely distinct from that of class I. Thus, findings on editing by class I synthetases may not be applicable generally to class II enzymes. Class II Escherichia coli proline-tRNA synthetase is shown here to misactivate alanine and to hydrolyze the noncognate amino acid before transfer to tRNA(Pro). This enzyme also is capable of rapidly deacylating a mischarged Ala-tRNA(Pro) variant. A single cysteine residue (C443) that is located within the class II-specific motif 3 consensus sequence was shown previously to be dispensable for proline-tRNA synthetase aminoacylation activity. We show here that C443 is critical for the hydrolytic editing of Ala-tRNA(Pro) by this class II synthetase.

Amino Acyl-tRNA Synthetases↗

PubMed1999

NMR structure of the (52-96) C-terminal domain of the HIV-1 regulatory protein Vpr: molecular insights into its biological functions.

The HIV-1 regulatory protein Vpr (96 amino acid residues) is incorporated into the virus particle through a mechanism involving its interaction with the C-terminal portion of Gag. Vpr potentiates virus replication by interrupting cell division in the G2 phase and participates in the nuclear transport of proviral DNA. The domain encompassing the 40 C-terminal residues of Vpr was shown to be involved in cell cycle arrest and binding of nucleocapsid protein NCp7, and suggested to promote nuclear provirus transfer. Accordingly, we show here that the synthetic 52-96 but not 1-51 sequences of Vpr interact with HIV-1 RNA. Based on these results, the structure of (52-96)Vpr was analysed by two-dimensional 1H-NMR in aqueous TFE (30%) solution and refined by restrained molecular dynamics. The structure is characterized by a long (53-78) amphipathic alpha-helix, followed by a less defined (79-96) C-terminal domain. The Leu60 and Leu67 side-chains are located on the hydrophobic side of the helix, suggesting their involvement in Vpr dimerization through a leucine zipper-type mechanism. Accordingly, their replacement by Ala eliminates Vpr dimerization in the two hybrid systems, while mutations of Ile74 and Ile81 have no effect. This was confirmed by gel filtration measurements and circular dichroism, which also showed that the alpha-helix still exists in (52-96)Vpr and its Ala60, Ala67 mutant in the presence and absence of TFE. Based on these results, a model of the coiled-coil Vpr dimer has been described, and its biological relevance as well as that of the structural characteristics of the 52-96 domain for the different functions of Vpr, including HIV-1 RNA binding, are discussed.

Amino Acid Sequence↗

PubMed1992

The role of anticodon bases and the discriminator nucleotide in the recognition of some E. coli tRNAs by their aminoacyl-tRNA synthetases.

The T7 polymerase transcription system was used for in vitro synthesis of unmodified versions of the E. coli tRNA mutants that insert asparagine, cysteine, glycine, histidine, and serine. These tRNAs were used to qualitatively explore the role of some anticodon bases and the discriminator nucleotide in the recognition of tRNA by aminoacyl-tRNA synthetases. Coupled with data from earlier studies, these new results essentially complete a survey of all E. coli tRNAs with respect to the involvement of anticodon bases and the discriminator nucleotide in tRNA recognition. It is found that in the vast majority of tRNAs both of these elements are significant components of tRNA identity. This is not universally true, however. Anticodon sequences are unimportant in tRNA(Ser), tRNA(Leu), and tRNA(Ala) while the discriminator base is inconsequential in tRNA(Ser) and tRNA(Thr). The significance of these results for origin-of-life studies is discussed.

Amino Acyl-tRNA Synthetases↗

PubMed1992

Correlation analysis of amino acid usage in protein classes.

We present a comparative study of residue usage correlations of various organism protein sets of diverse phylogenetic species and of open reading frames of several large human viral genomes. Our correlation analysis reveals three major tendencies: (i) charge compensation reflected by the high correlation of basic with acidic residues; (ii) the positive correlations of functionally and structurally similar amino acids including many pairs of hydrophobic amino acids, all pairs of aromatic amino acids, the anionic pair (glutamate and aspartate), but not the cationic pair (lysine and arginine), moderately the hydroxyl pair (serine and threonine), the small amino acids (glycine and alanine), and many (but not all) of those having high values in the Dayhoff substitutability matrix (characteristics such as amino acid polarity or codon usage agreement, except for the wobble position, do not necessarily imply significant positive correlations); (iii) a widespread negative correlation of the aggregate strong codon group amino acids (Ala, Gly, Pro) versus the weak codon group amino acids (Lys, Ile, Tyr, Asn, Phe). Discussion and speculations relate amino acid usage correlations to protein function/structure, cellular localization, proximity in amino acid biosynthetic pathways, amino acid relative abundances, tRNA and aminoacyl synthetase availabilities, and evolutionary processes.

Amino Acids↗

PubMed2002

Quality control of translation through the kinetic discrimination of tRNAs in the network of aminoacyl-tRNA synthetases.

It is known that each aminoacyl-tRNA synthetase (aaRS) specifically recognizes its cognate tRNAs to ensure the correct translation of the genetic information. However, we had previously demonstrated that mammalian mitochondrial seryl-tRNA synthetase (mt SerRS) can markedly misacylate mitochondrial (mt) tRNA(Gln). To investigate extensively misacylation reactions in mammalian mitochondrion, we purified overall twenty-two mt tRNAs from bovine liver, and determined their misacylation activities using mt SerRS. In addition to tRNA(Gln), tRNA(Ala) and tRNA(Asn) showed weak but significant serylation activities, which raises the possibility that each mammalian mt aaRS can misacylate several non-cognate mt tRNAs in varying degrees, but translational fidelity might be maintained by kinetic discrimination of tRNAs in the network of aaRSs.

Amino Acyl-tRNA Synthetases↗

PubMed1995

Effects of cavity-creating mutations on conformational stability and structure of the dimeric 4-alpha-helical protein ROP: thermal unfolding studies.

The structural and energetic perturbations caused by cavity-creating mutations (Leu-41-->Val and Leu-41-->Ala) in the dimeric 4-alpha-helical-bundle protein ROP have been characterized by CD spectroscopy and differential scanning calorimetry (DSC). Deconvolution of the CD spectra showed a decrease in alpha-helicity as a result of the amino acid exchanges that follows qualitatively the overall decrease in conformational stability. Transition enthalpies are sensitive probes of the energetic change associated with point mutations. delta H zero values at the respective transition temperatures, T 1/2 (71.0, 65.3, and 52.9 degrees C at 0.5 mg/ml) decrease from 580 +/- 20 to 461 +/- 20 kJ/(mol of dimer) and 335 +/- 20 kJ/(mol of dimer) for wild-type ROP (Steif, C., Weber, P., Hinz, H.-J., Flossdorf, J., Cesareni, G., Kokkinidis, M. Biochemistry 32:3867-3876, 1993), L41V, and L41A, respectively. The conformational stabilities at 25 degrees C expressed by the standard Gibbs energies of denaturation, delta GzeroD, are 71.7, 61.1, and 46.1 kJ/(mol of dimer). The corresponding transition enthalpies have been obtained from extrapolation using the cDp(T) and cNp(T) functions. Their values at 25 degrees C are 176.3, 101.9, and 141.7 kJ/(mol of dimer) for wild-type ROP, L41V, and L41A, respectively. When the stability perturbation resulting from the cavity creating mutations is referred to the exchange of 1 mol of CH2 group, the average delta delta GzeroD value is -5.0 +/- 1 kJ/(mol of CH2 group). This decrease in conformation stability suggests that dimeric ROP exhibits the same susceptibility to Leu-->Val and Leu-->Ala exchanges as small monomeric proteins. Careful determinations of the partial specific heat capacities of wild-type and mutated protein solutions suggest that the mutational effects are predominantly manifested in the native rather than the unfolded state.

Alanine↗

PubMed1994

Role of the TIGN sequence in E. coli tryptophanyl-tRNA synthetase.

Tryptophanyl-tRNA synthetase in E. coli does not have the HIGH sequence that is normally characteristic of class I aminoacyl-tRNA synthetases (EC 6.1.1.2), but instead contains a TIGN sequence at residues 17-20, which has been suggested to be equivalent to the HIGH sequence (Jones, M.D. et al. (1986) Biochemistry 25, 1887-1891). We have overexpressed E. coli Trp-tRNA synthetase and have used site-directed mutagenesis to mutate Thr-17 in the TIGN sequence to alanine. The mutant enzyme has the same Km values as the wild-type for tryptophan or tRNA(Trp), and a slightly increased Km for ATP, from 0.37 to 0.64 mM. On the other hand, the kcat for either the first step or the overall reaction is decreased by a factor of 30. In comparing the Thr-17 and Ala-17 enzymes, the delta delta G for the conversion of substrate to transition state is +9.6 kJ/mol (2.3 kcal/mol). Thr-17 is therefore important in binding the substrate in the transition state, thus supporting the suggestion that TIGN may fulfill the role of a HIGH sequence.

Amino Acid Sequence↗

PubMed1985

Fine structure-activity analysis of mutations at position 51 of tyrosyl-tRNA synthetase.

Residue Thr-51 at the active site of tyrosyl-tRNA synthetase (Bacillus stearothermophilus) has been replaced with all the smaller amino acids by protein engineering to investigate direct and indirect effects of mutation on substrate binding and catalysis. The gamma-hydroxyl group of Thr-51 was thought to be 0.5 A too far from the ribose ring oxygen of ATP to form a hydrogen bond. Consistent with this, it is found that mutation of Thr-51----Cys-51, which should place the gamma-thiol group within its correct distance for hydrogen bonding, increases the affinity of the enzyme for ATP. Other mutations (Ser-51, Ala-51, and Gly-51) show the contributions to binding of the other atoms in the side chain of Thr-51. A family of enzymes has been produced, TyrTS(Thr-51) (wild type), TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51), in which the value of kcat/KM for ATP in aminoacylation increases along the series. This is achieved by the value of KM decreasing significantly (2.5, 1.25, 0.29, and 0.019 mM, respectively) while there are smaller decreases in kcat (4.7, 4.0, 2.9, and 1.8 s-1, respectively). These variations cause each one of the enzymes to be more active than the others at particular concentrations of ATP. For example, at concentrations of ATP greater than 5.9 mM, TyrTS(Thr-51) is the most active, while TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51) are the most active at 5.9-2.2, 2.2-0.42, and less than 0.42 mM ATP, respectively. Interestingly, position 51 shows variation in tyrosyl-tRNA synthetases isolated from different organisms.

Adenosine Triphosphate↗

PubMed2005

Structural basis for non-cognate amino acid discrimination by the valyl-tRNA synthetase editing domain.

The editing domain of valyl-tRNA synthetase (ValRS) is known to deacylate, or edit, misformed Thr-tRNA(Val) (post-transfer editing). Here, we determined the 1.7-Angstroms resolution crystal structure of the Thermus thermophilus ValRS editing domain. A comparison of the structure with the previously reported tRNA complex structure revealed conformational changes of the editing domain upon accommodation of the terminal A76; the "GTG loop" moves to expand the pocket, and the side chain of Phe-264 on the GTG loop rotates to interact with the A76 adenine ring. If these conformational changes did not occur, then C75 and A76 of the tRNA would clash with Phe-264. To elucidate the mechanism of the threonine side-chain recognition, we determined the crystal structure of the editing domain bound with [N-(L-threonyl)-sulfamoyl]adenosine at 1.7-Angstroms resolution. The gamma-OH of the threonyl moiety is recognized by the Lys-270, Thr-272, and Asp-279 side chains, which may reject the cognate valyl moiety. Accordingly, ValRS mutants with an Ala substitution for Lys-270 or Asp-279 synthesized significant amounts of Thr-tRNA(Val). The misproduced Thr-tRNA(Val) was hydrolyzed efficiently by the wild-type ValRS, but this post-transfer editing activity was drastically impaired by the Ala substitutions for Lys-270 and Asp-279 and was also decreased by those for Arg-216, Phe-264, and Thr-272. These results indicate that the threonyl moiety and A76 of Thr-tRNA(Val) are recognized by the Lys-270, Thr-272, and Asp-279 side chains and by the Phe-264 side chain, respectively, of the ValRS editing domain.

Amino Acid Sequence↗

PubMed1972

Inhibition by elongation factor EF G of aminoacyl-tRNA binding to ribosomes.

Elongation factor G (EF G), bound to ribosomes either with GMPPCP or with fusidic acid and GDP, inhibits elongation factor Tu (EF Tu)-dependent binding of Phe-tRNA on the ribosome-poly(U) complex and binding of Ala-tRNA on the initiation complex formed with RNA from bacteriophage R17; GTP hydrolysis associated with Phe-tRNA binding is also inhibited. Moreover, nonenzymic binding of Phe-tRNA at high Mg(++) concentration is completely blocked by EF G. Thus, EF G appears to bind at a site that overlaps or interacts with the ribosomal A-site.

Amino Acids↗

PubMed2006

Differential role for cyclic AMP response element binding protein-1 in multiple stages of B cell development, differentiation, and survival.

CREB-1 is expressed in the bone marrow and in developing B cells. To determine the role of CREB-1 in developing B cells in the bone marrow, several lines of transgenic (Tg) mice overexpressing a dominant-negative Ser(119-ala) phosphomutant CREB-1 in the bone marrow were generated. Analysis of RNA and protein revealed expression of the transgene in the bone marrow. Flow cytometric analysis of bone marrow cells from Tg mice revealed approximately 70% increase in pre-B1 (CD43(+)B220(+)CD24(+(int))) and approximately 60% decreased pre-BII (CD43(+)B220(+)CD24(++(high))) cells, indicating a developmental block in pre-BI to pre-BII transition. Consistent with this, the Tg mice showed approximately 4-fold decrease in immature and mature B cells in the bone marrow. RT-PCR analysis of RNA from Tg mice revealed increased JunB and c-Jun in pre-BII cells associated with decreased S-phase entry. Adoptive transfer of bone marrow cells into RAG-2(-/-) mice resulted in reconstitution of non-Tg but not Tg bone marrow-derived CD43(+)B220(+)CD24(high) population that is normally absent in RAG-2(-/-) mice. In the periphery, the Tg mice exhibited decreased CD21(dim)CD23(high)IgM(+) follicular B cells in the spleen and increased B1a and B1b B cells in the peritoneum. While exhibiting normal Ab responses to T-independent Ags and primary response to the T-dependent Ag DNP-keyhole limpet hemocyanin, the Tg mice exhibited severely impaired secondary Ab responses. These studies provide the first evidence for a differential role for CRE-binding proteins in multiple stages of B cell development, functional maturation, and B1 and B2 B cells.

Animals↗

PubMed1990

Expression of the Synechocystis sp. strain PCC 6803 tRNA(Glu) gene provides tRNA for protein and chlorophyll biosynthesis.

In the cyanobacterium Synechocystis sp. strain PCC 6803 (Synechocystis 6803) delta-aminolevulinic acid (ALA), the sole precursor for the synthesis of the porphyrin rings of heme and chlorophyll, is formed from glutamate activated by acylation to tRNA(Glu) (G. P. O'Neill, D. M. Peterson, A. Schön, M. W. Chen, and D. Söll, J. Bacteriol. 170:3810-3816, 1988; S. Rieble and S. I. Beale, J. Biol. Chem. 263:8864-8871, 1988). We report here that Synechocystis 6803 possesses a single tRNA(Glu) gene which was transcribed as monomeric precursor tRNA and matured into the two tRNA(Glu) species. They differed in the extent of modification of the first anticodon base, 5-methylaminomethyl-2-thiouridine (O'Neill et al., 1988). The two tRNA species had equivalent capacities to stimulate the tRNA-dependent formation of ALA in Synechocystis 6803 and to provide glutamate for protein biosynthesis in an Escherichia coli-derived translation system. These results are in support of a dual role of tRNA(Glu). The levels of tRNA(Glu) were examined by Northern (RNA) blot analysis of cellular RNA and by aminoacylation assays in cultures of Synechocystis 6803 in which the amount of chlorophyll synthesized was modulated over a 10-fold range by various illumination regimens or by the addition of inhibitors of chlorophyll and ALA biosynthesis. In these cultures, the level of tRNA(Glu) was always a constant fraction of the total tRNA population, suggesting that tRNA(Glu) and chlorophyll levels are regulated independently. In addition, the tRNA(Glu) was always fully aminoacylated in vivo.

Aminolevulinic Acid↗

PubMed2005

Effects of di-(2-ethylhexyl)-phthalate (DEHP) and its metabolites on fatty acid homeostasis regulating proteins in rat placental HRP-1 trophoblast cells.

Di-(2-ethylhexyl)-phthalate (DEHP) is a widely used plasticizer and ubiquitous environmental contaminant. The potential health hazards, including teratogenicity, from exposure to DEHP may be related to the role of DEHP or its metabolites in the trans-activation of peroxisome proliferator-activated receptors (PPARs). Fetal essential fatty acid (EFA) homeostasis is controlled by directional transfer across the placenta through a highly regulated process, including PPAR activation. Using HRP-1 rat trophoblastic cells, the effects of DEHP and two of its metabolites, mono-(2-ethylhexyl)-phthalate (MEHP) and 2-ethylhexanoic acid (EHA), on the mRNA and protein expression of the three known PPAR isoforms (alpha, beta, and gamma), fatty acid transport protein 1 (FATP1), plasma membrane fatty acid binding protein (FABPpm), and the heart cytoplasmic fatty acid binding protein (HFABP) were investigated. This study also investigated the functional effects of exposure on the uptake and transport of six long chain fatty acids (LCFAs): arachidonic acid (AA), docosahexaenoic acid (DHA), linoleic acid (LA), alpha-linolenic acid (ALA), oleic acid (OA), and stearic acid (SA). In the presence of DEHP, MEHP, and EHA, the expression of PPARalpha, PPARgamma, FATP1, and HFABP were up-regulated in a dose- and time- dependent manner, while PPARbeta and FABPpm demonstrated variable expression. The uptake rates of EFAs (AA, DHA, LA, ALA) increased significantly upon exposure, and the transport of AA (omega-6) and DHA (omega-3) were directionally induced. These results suggest that DEHP, MEHP, and EHA can influence EFA transfer across HRP-1 cells, implying that these compounds may alter placental EFA homeostasis and potentially result in abnormal fetal development.

Animals↗