[The complete chemical synthesis of L-C14-serine-ethanolamine and L-C14 threonine-ethanolamine phosphodiesters].
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Amino Alcohols↗
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[Biological significance and metabolic aspects of L-serine-ethanolamine and L-threonine-ethanolamine phosphodiesters].
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Amino Alcohols↗
[Preliminary data on the organic synthesis of L-serine-ethanolamine ad L-threonine-ethanolamine phosphodiesters labeled with C-14].
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Amino Alcohols↗
Ethanolamine metabolism in cultured bovine aortic endothelial cells.
The role of extracellular ethanolamine in phospholipid synthesis was examined in cultured bovine aortic endothelial cells. Serine and ethanolamine were both readily accumulated by these cells and incorporated into phospholipid. Exposing cells to extracellular ethanolamine for 4-6 weeks had no effect on cell growth, yet increased the phosphatidylethanolamine content of these cells by 31% as compared to control cells. The intracellular content of ethanolamine was measured by high performance liquid chromatography, and results showed that the ethanolamine-treated cells contained a significantly greater amount of free ethanolamine compared to control cells (0.62 +/- 0.07 nmol/mg of protein versus 0.27 +/- 0.05 nmol/mg of protein, respectively). Ethanolamine-treated cells also had decreased accumulation and incorporation into lipid of [3H]ethanolamine throughout a 48-h incubation and increased K'm and V'max parameters of ethanolamine transport as compared to control cells. Studies were also done to examine the effect of ethanolamine on the generation of free ethanolamine from phosphatidylserine. In pulse-chase experiments with [3H]serine, a physiological concentration of ethanolamine (25 microM) decreased the amount of 3H-labeled phosphatidylethanolamine produced from 3H-labeled phosphatidylserine by 12 h as compared to the amount of 3H-labeled phosphatidyl-ethanolamine produced in the absence of ethanolamine in the chase incubation. Furthermore, ethanolamine-treated cells accumulated 20% less labeled ethanolamine in the aqueous pool from [3H]serine after 24 h of incubation than did control cells. These results can be explained by isotope dilution with the ethanolamine pool that accumulates in these cells with time when exposed to media supplemented with a physiological concentration of ethanolamine and by an effect of ethanolamine on ethanolamine generation from phosphatidylserine. The results show that an extracellular source of ethanolamine significantly influences the phospholipid metabolism of cultured bovine aortic endothelial cells.
Animals↗
Modulation of phosphatidylethanolamine biosynthesis by exogenous ethanolamine and analogues in the hamster heart.
In the hamster heart, exogenous ethanolamine is taken up by the heart and utilized for the biosynthesis of phosphatidylethanolamine. The role of the exogenous supply of ethanolamine on phosphatidylethanolamine biosynthesis was examined by perfusing hamster heart with various concentrations of labelled ethanolamine. Analysis of the radioactivity distributed in the ethanolamine-containing metabolites indicated that at low exogenous ethanolamine concentrations (< or = 0.1 microM), the conversion of phosphoethanolamine to CDP-ethanolamine was rate-limiting for phosphatidylethanolamine biosynthesis. However, perfusion with higher concentrations of ethanolamine (> or = 0.4 microM) resulted in the phosphorylation of ethanolamine becoming rate-limiting. Since the intracellular ethanolamine levels remained unchanged, the alterations in radioactivity distribution suggested that the newly imported ethanolamine was preferentially utilized for phosphatidylethanolamine biosynthesis. The effects of ethanolamine analogues on ethanolamine uptake and subsequent conversion to phosphatidylethanolamine at physiological concentrations of exogenous ethanolamine were examined. Monomethylethanolamine was found to inhibit ethanolamine uptake, the conversion of ethanolamine to phosphoethanolamine and incorporation of radioactivity into phosphatidylethanolamine. The accumulation of radioactivity in the ethanolamine fraction by monomethylethanolamine, despite of the inhibition of ethanolamine uptake, further confirms the rate-limiting role of ethanolamine kinase in the biosynthesis of phosphatidylethanolamine.
Alanine↗
Newly imported ethanolamine is preferentially utilized for phosphatidylethanolamine biosynthesis in the hamster heart.
The effects of exogenous ethanolamine concentrations on ethanolamine uptake and its subsequent incorporation into phosphatidylethanolamine were examined. Hamster hearts were perfused with 0.04-1000 microM labelled ethanolamine. Analysis of radioactivity distribution in ethanolamine-containing metabolites revealed an accumulation of labelled ethanolamine when the heart was perfused with greater than or equal to 0.4 microM labelled ethanolamine. The changes in radioactivity distribution indicated that the phosphorylation of ethanolamine had become rate-limiting in the CDP-ethanolamine pathway when the heart was perfused with greater than or equal to 0.4 microM ethanolamine. Perfusion with different concentrations of ethanolamine did not significantly change the intracellular ethanolamine pool. The accumulation of labelled ethanolamine without a corresponding change in the ethanolamine pool suggests that the newly imported ethanolamine did not equilibrate with the endogenous ethanolamine pool. We postulate that the newly imported ethanolamine was preferentially utilized for phosphatidylethanolamine biosynthesis.
Animals↗
Ethanolamine transport in human placental brush-border membrane vesicles.
Pathways for transport of ethanolamine by human placental epithelia were investigated by measurement of [3H]ethanolamine uptake in brush-border membrane vesicles isolated by divalent cation precipitation. The presence of a conductive uptake pathway for ethanolamine was suggested by the marked stimulation of ethanolamine uptake to levels exceeding equilibrium induced by an inside-negative potassium diffusion potential. Evidence to suggest conductive ethanolamine uptake resulted from a mediated transport process included 1) the concentration-dependent inhibition by choline; 2) trans-stimulation of choline and ethanolamine uptake by ethanolamine; and 3) substrate-specific inhibition by chemically related analogs. Transport of both choline and ethanolamine by a common facilitated diffusion mechanism is suggested by 1) trans-stimulation of choline uptake by ethanolamine; 2) mutual inhibition of conductive choline and ethanolamine uptake by ethanolamine and choline; 3) the effect of ethanolamine on the kinetics of conductive choline uptake; and 4) the rank order inhibition of choline and ethanolamine uptake by the same panel of chemical analogs. The present study identifies the presence of a facilitated diffusion mechanism as a brush-border membrane transport pathway for choline and ethanolamine accumulation by human placenta.
Adult↗
Functions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium.
When B12 is available, Salmonella typhimurium can degrade ethanolamine to provide a source of carbon and nitrogen. B12 is essential since it is a cofactor for ethanolamine ammonia-lyase, the first enzyme in ethanolamine breakdown. S. typhimurium makes B12 only under anaerobic conditions; in the presence of oxygen, exogenous B12 must be provided to permit ethanolamine utilization. Genes required for ethanolamine utilization are encoded in the eut operon. For complementation testing, an F' plasmid containing the eut genes was constructed by transposition of the eut operon (flanked by two Tn10 elements) to an existing F plasmid. Complementation tests defined six genes in the eut operon. Three of these genes encode enzymes known to be involved in degradation of ethanolamine: ethanolamine ammonia-lyase (eutB and eutC) and acetaldehyde dehydrogenase (eutE). One gene (eutR) seems to encode a positive regulatory protein required for induction of transcription of eut. The function of one of the remaining two genes (eutA) was shown to be required for ethanolamine utilization only when cyano-B12 or hydroxy-B12 were the precursors of the adenosyl-B12 cofactor of ethanolamine ammonia-lyase; eutA mutants could use ethanolamine as the nitrogen source only when adenosyl-B12 was provided. No function has been assigned to the eutD gene, which is required for use of ethanolamine as a carbon source. Ethanolamine uptake assays of eut mutants suggest that no ethanolamine permease is encoded in the eut operon.
Biological Transport↗
Minimal functions and physiological conditions required for growth of salmonella enterica on ethanolamine in the absence of the metabolosome.
During growth on ethanolamine, Salmonella enterica synthesizes a multimolecular structure that mimics the carboxysome used by some photosynthetic bacteria to fix CO(2). In S. enterica, this carboxysome-like structure (hereafter referred to as the ethanolamine metabolosome) is thought to contain the enzymatic machinery needed to metabolize ethanolamine into acetyl coenzyme A (acetyl-CoA). Analysis of the growth behavior of mutant strains of S. enterica lacking specific functions encoded by the 17-gene ethanolamine utilization (eut) operon established the minimal biochemical functions needed by this bacterium to use ethanolamine as a source of carbon and energy. The data obtained support the conclusion that the ethanolamine ammnonia-lyase (EAL) enzyme (encoded by the eutBC genes) and coenzyme B(12) are necessary and sufficient to grow on ethanolamine. We propose that the EutD phosphotransacetylase and EutG alcohol dehydrogenase are important to maintain metabolic balance. Glutathione (GSH) had a strong positive effect that compensated for the lack of the EAL reactivase EutA protein under aerobic growth on ethanolamine. Neither GSH nor EutA was needed during growth on ethanolamine under reduced-oxygen conditions. GSH also stimulated growth of a strain lacking the acetaldehyde dehydrogenase (EutE) enzyme. The role of GSH in ethanolamine catabolism is complex and requires further investigation. Our data show that the ethanolamine metabolosome is not involved in the biochemistry of ethanolamine catabolism. We propose the metabolosome is needed to concentrate low levels of ethanolamine catabolic enzymes, to keep the level of toxic acetaldehyde low, to generate enough acetyl-CoA to support cell growth, and to maintain a pool of free CoA.
Acetaldehyde↗
Ethanolamine and choline transport in cultured bovine aortic endothelial cells.
The transport of the polar head groups, ethanolamine and choline, was examined in cultured bovine aortic endothelial cells. Both ethanolamine and choline are taken up by high- and low-affinity systems. The K'm and V'max for the Na+-dependent, high-affinity ethanolamine and choline transport system are 3.0 and 3.0 microM and 5.4 and 7.3 pmol/mg protein/min, respectively. Ethanolamine and choline competitively influence one another's transport as the presence of 50 microM ethanolamine increases the K'm but not the V'max of choline uptake. Likewise, 50 microM choline increases the K'm but not the V'max of ethanolamine transport. The concentration of ethanolamine that inhibits maximal velocity of 5 microM choline by 50% is 9.7 microM, while 12 microM choline inhibits 5 microM ethanolamine maximal velocity by 50%. Uptake of both head groups is only partially Na+-dependent and is inhibited similarly by 2-methylethanolamine and 2,2-dimethylethanolamine at all concentrations examined. Hemicholinium-3, a classic inhibitor of high-affinity, Na+-dependent choline transport, reduces both ethanolamine and choline accumulation in a concentration-dependent fashion, but has a greater effect on choline transport at higher concentrations. The major portion of these data is consistent with our hypothesis that the uptake of physiological concentrations of ethanolamine and choline may occur through the same transport system. However, the results of the effect of hemicholinium-3 and the extent of Na+-dependency of choline and ethanolamine uptake could be interpreted as meaning that separate transport systems for choline and ethanolamine exist which cross react or that a single transport system exists which has separate active sites for the two compounds.
Animals↗
Comparison of the hydrolysis of phosphatidylethanolamine and phosphatidyl(N-acyl)ethanolamine in Dictyostelium discoideum amoebae.
In Dictyostelium discoideum, (N-acyl)ethanolamine glycerophospholipids disappear as the amoebae aggregate, whereas the amount of ethanolamine glycerophospholipids remains relatively constant, suggesting that each type of ethanolamine-containing phospholipid might have a separate metabolic pathway. To study their metabolism, phosphatidylethanolamine and phosphatidyl(N-acyl)ethanolamine containing either [14C]ethanolamine or a 14C-labeled sn-2 fatty acyl group were incubated with D. discoideum homogenates, and the conversion of the substrates into radioactive products was monitored. At pH values 3.8 and 4.5, phosphatidyl(N-acyl)ethanolamine was hydrolyzed by a phospholipase A1 to form the sn-2 acyl form of the lipid. Only minor hydrolysis occurred at pH values of 5.2 or higher. (N-acyl)Ethanolamine was also released by a phospholipase D type activity at 0.1 the rate of the lysophospholipid formation. Phosphatidyl(N-acyl)ethanolamine was not hydrolyzed to form phosphatidylethanolamine or water soluble components. At pH 7.2 and at the low pH range of 3.8-4.5, phosphatidylethanolamine was hydrolyzed to lysophosphatidylethanolamine, which was then further degraded to water-soluble components. At pH 7.2, a phospholipase A2 initially hydrolyzed the phosphatidylethanolamine, whereas at the low pH range a phospholipase A1 was the most active enzyme. Although both types of ethanolamine-containing phospholipid were hydrolyzed by a phospholipase A1 at the low pH range, phosphatidylethanolamine hydrolysis was more sensitive to inhibition by Trition X-100, and phosphatidylethanolamine was hydrolyzed to water-soluble components, whereas phosphatidyl(N-acyl)ethanolamine was not. At pH 7.2, phosphatidylethanolamine was hydrolyzed, but phosphatidyl(N-acyl)ethanolamine was not hydrolyzed at all. These results indicate that there are separate routes of degradation for the two types of ethanolamine-containing phospholipid in D. discoideum.
Carbon Radioisotopes↗
Depolarization-induced release of ethanolamine from brain synaptic preparations in vitro.
The release of ethanolamine from mouse brain synaptosomes and synaptoneurosomes has been investigated. The depolarizing agents veratridine (50 microM), KCl (35 mM) and 4-aminopyridine (2 mM) enhanced the release of [3H]ethanolamine from preloaded synaptosomes under superfusion conditions. Tetrodotoxin (2 microM) strongly inhibited veratridine- and 4-aminopyridine-stimulated release of [3H]ethanolamine but had no effect on KCl-evoked or resting release. In the absence of calcium, a reduction in the resting release of [3H]ethanolamine occurred and release evoked by veratridine, and KCl was markedly reduced. Exposure of preloaded synaptosomes to 5 mM ethanolamine (but not 5 mM serine or 5 mM choline) calcium-dependently increased the efflux of [3H]ethanolamine, however, this was not accompanied by membrane depolarization. When these experiments were performed using synaptoneurosomes, qualitatively similar results were obtained. The resting and evoked release of [3H]ethanolamine was however approximately 2.5-fold higher compared to synaptosomes on a brain equivalent basis, suggesting that uptake and release occur at sites in addition to the nerve ending. Our data are consistent with the idea that a significant amount of ethanolamine accumulates presynaptically and undergoes calcium-dependent release upon depolarization possibly via classical exocytosis. In contrast, ethanolamine-induced release of [3H]ethanolamine likely involves mostly diffusional exchange across the neuronal membrane rather than base exchange. The present results add support to the concept that ethanolamine may play a role as a synaptic signaling molecule in mammalian brain.
4-Aminopyridine↗
Limited metabolic interaction of serine with ethanolamine and choline in the turnover of phosphatidylserine, phosphatidylethanolamine and plasmalogens in cultured glioma cells.
Modulation of choline phosphoglyceride turnover has been investigated extensively but less is known about regulation of serine and ethanolamine phosphoglyceride synthesis and turnover. We investigated incorporation and interactions of [3H(G)]L-serine, [1,2-14C]ethanolamine and [methyl-3H]choline in cultured glioma cells. Exogenous serine did not compete with ethanolamine or choline incorporation and did not chase labeled headgroup from ethanolamine phosphoglycerides (PE); serine displaced headgroup of prelabeled phosphatidylserine (PtdSer) resulting in less labeled PtdSer for decarboxylation. In contrast, exogenous ethanolamine markedly chased labeled headgroup of non-plasmenylethanolamine phosphoglycerides (NP-PE) with less effect on plasmalogen (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) whether headgroup was derived from [3H]serine or [14C]ethanolamine. Label in chase medium was mainly ethanolamine to 12 h; phosphoethanolamine was present with longer chase (12-48 h). Choline did not compete with serine incorporation and had little chase effect on PtdSer and PE. Choline and ethanolamine competitively interacted with preference for choline. These data suggest that (1) PtdSer synthesis in cultured glioma cells may involve more than headgroup exchange; (2) PE turnover with metabolite release to medium may involve both phospholipase D and phospholipase C; (3) acceleration of PE turnover by exogenous ethanolamine primarily involves NP-PE with lesser involvement of plasmalogen; and (4) in contrast to lack of interaction between serine and other headgroup precursors, choline and ethanolamine compete primarily at uptake.
Animals↗
Phosphatidylethanolamine metabolism in rat liver after partial hepatectomy. Control of biosynthesis of phosphatidylethanolamine by the availability of ethanolamine.
The effect of partial (70%) hepatectomy on phosphatidylethanolamine (PE) synthesis was studied in rat liver during the first 4 post-operative days. Between 4 and 96 h after partial hepatectomy, the mass of PE increased from 30% to 80% of sham-operation values. In line with the increase in PE mass, the rate of PE synthesis in vivo from [14C]ethanolamine was stimulated 1.6- and 1.3-fold at 22 and 48 h after partial hepatectomy respectively. Surprisingly, the activity of CTP:phosphoethanolamine cytidylyltransferase (EC 2.7.7.14) was virtually unchanged after partial hepatectomy. In addition, neither ethanolamine kinase (EC 2.7.1.82) nor ethanolaminephosphotransferase (EC 2.7.8.1) showed any changes in activity over the time period studied. Hepatic levels of ethanolamine and phosphoethanolamine were drastically increased after partial hepatectomy, as compared with sham operation, whereas levels of CDP-ethanolamine and microsomal diacylglycerol were not affected. Interestingly, partial hepatectomy caused the concentration of free ethanolamine in serum to increase from 29 microM to approx. 50 microM during the first day after surgery. In hepatocytes isolated from non-operated animals, incorporation of [3H]ethanolamine into PE was stimulated by increasing the ethanolamine concentration from 10 up to 50 microM, whereas the radioactivity associated with phosphoethanolamine only increased at ethanolamine concentrations higher than 30 microM. Taken together, our results indicate that the observed increase in serum ethanolamine concentration after partial hepatectomy is probably responsible for both the increase in PE biosynthesis and the accumulation of ethanolamine and phosphoethanolamine in regenerating liver.
Animals↗
Specificity of ethanolamine transport and its further metabolism in Trypanosoma brucei.
Ethanolamine is found in trypanosomes as an integral component of the variant surface glycoprotein (VSG) and the membrane phospholipid phosphatidylethanolamine (PE). Steps in the utilization of ethanolamine could represent novel targets for the development of chemotherapeutic drugs and were therefore investigated in detail. Transport of [3H]ethanolamine was studied using structural analogs of ethanolamine. Compounds with substitutions in the amino group or of one of the methylene hydrogens of ethanolamine were the most effective inhibitors. Those analogs studied in detail with respect to their kinetic properties were all found to be competitive inhibitors of ethanolamine transport. Following uptake, ethanolamine is rapidly phosphorylated by an ethanolamine-specific kinase to form phosphoethanolamine. Other acid-soluble intermediates identified by thin layer chromatography were CDP-ethanolamine, dCDP-ethanolamine, and glycerophosphorylethanolamine. The relative amounts of these metabolites varied between slender (dividing) and stumpy (non-dividing) trypanosomes and may reflect special biosynthetic needs of the different morphological forms. Pulse-chase experiments indicated that the acid-soluble metabolites served as precursors for chloroform/methanol-soluble lipids. Radioactive lipids included PE, mono-methyl and dimethyl PE, and lysoPE. Further methylation of dimethylPE to phosphatidylcholine was not observed under the experimental conditions described. These results are consistent with the conclusion that trypanosomes are able to synthesize phospholipids via the Kennedy pathway.
Animals↗
Effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney-21 cells.
The effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney (BHK-21) cells were investigated. The cells were incubated with labelled choline in the presence of an amino acid or ethanolamine. The uptake of labelled choline was noncompetitively inhibited by amino acids. Glycine, L-alanine, L-serine, L-leucine, L-aspartate, and L-arginine were effective inhibitors and a maximum of 22% inhibition of choline uptake was obtained with 5 mM glycine. Analyses of the labelings in the choline-containing metabolites revealed that the conversion of choline to CDP-choline and subsequently phosphatidylcholine was not affected by the presence of amino acids. The uptake of choline was also inhibited by ethanolamine in a concentration-dependent manner. Kinetic studies on the uptake of choline indicated that the inhibition by ethanolamine was competitive in nature. Although ethanolamine is a potent inhibitor of choline kinase, analyses of the labelings in the choline-containing metabolites indicated that the conversion of choline to phosphocholine was not affected in the cells incubated with ethanolamine. Ethanolamine did not change the pool sizes of phosphocholine and CDP-choline. Based on the specific radioactivity of CDP-choline and the labeling of phosphatidylcholine, the rates of phosphatidylcholine biosynthesis were not significantly different between the control and the ethanolamine-treated cells. In view of the concentrations of amino acids (millimolar) and ethanolamine (micromolar) in most cell culture media, it appeared that only amino acids were important metabolites for the regulation of choline uptake in BHK-21 cells. We conclude that both amino acids and ethanolamine have no direct effect on the biosynthesis of phosphatidylcholine.
Amino Acids↗
Effect of ethanolamine on choline uptake and incorporation into phosphatidylcholine in human Y79 retinoblastoma cells.
The effect of physiological concentrations of ethanolamine on choline uptake and incorporation into phosphatidylcholine was investigated in human Y79 retinoblastoma cells, a multipotential, undifferentiated retinal cell line that has retained many neural characteristics. These cells have a high-affinity uptake system for choline, and the majority of the choline taken up was incorporated into phosphatidylcholine via the CDP-choline pathway. The presence of extracellular ethanolamine significantly decreased high-affinity choline uptake and, subsequently, the amount of choline incorporated into phosphatidylcholine. When 100 mumol/L ethanolamine was added, there was a decrease of about 8% in the phosphatidylcholine content. Ethanolamine had no effect on choline incorporation into phosphatidylcholine, however, once choline was taken up by the cell. The K'M and V'max for high-affinity choline uptake was increased from 0.93 to 9.74 microM and 19.60 to 79.25 pmol/min per mg protein, respectively, by the presence of 25 mumol/L ethanolamine. In contrast, 25 mumol/L choline had no effect on the kinetic parameters of high-affinity ethanolamine uptake. Therefore, the reduction in high-affinity choline transport by ethanolamine apparently is not simply due to competitive inhibition. 2,2-Dimethylethanolamine and 2-methylethanolamine both reduced choline uptake to a greater extent than ethanolamine. However, because these compounds exist at much lower concentrations than ethanolamine, they probably have little physiological influence. These results suggest that changes in ethanolamine concentration within the physiologic range can regulate the synthesis and content of phosphatidylcholine in a neural cell by influencing the uptake of choline.
Biological Transport↗
Isolation and characterization of the Saccharomyces cerevisiae EKI1 gene encoding ethanolamine kinase.
Ethanolamine kinase (ATP:ethanolamine O-phosphotransferase, EC 2.7.1. 82) catalyzes the committed step of phosphatidylethanolamine synthesis via the CDP-ethanolamine pathway. The gene encoding ethanolamine kinase (EKI1) was identified from the Saccharomyces Genome Data Base (locus YDR147W) based on its homology to the Saccharomyces cerevisiae CKI1-encoded choline kinase, which also exhibits ethanolamine kinase activity. The EKI1 gene was isolated and used to construct eki1Delta and eki1Delta cki1Delta mutants. A multicopy plasmid containing the EKI1 gene directed the overexpression of ethanolamine kinase activity in wild-type, eki1Delta mutant, cki1Delta mutant, and eki1Delta cki1Delta double mutant cells. The heterologous expression of the S. cerevisiae EKI1 gene in Sf-9 insect cells resulted in a 165,500-fold overexpression of ethanolamine kinase activity relative to control insect cells. The EKI1 gene product also exhibited choline kinase activity. Biochemical analyses of the enzyme expressed in insect cells, in eki1Delta mutants, and in cki1Delta mutants indicated that ethanolamine was the preferred substrate. The eki1Delta mutant did not exhibit a growth phenotype. Biochemical analyses of eki1Delta, cki1Delta, and eki1Delta cki1Delta mutants showed that the EKI1 and CKI1 gene products encoded all of the ethanolamine kinase and choline kinase activities in S. cerevisiae. In vivo labeling experiments showed that the EKI1 and CKI1 gene products had overlapping functions with respect to phospholipid synthesis. Whereas the EKI1 gene product was primarily responsible for phosphatidylethanolamine synthesis via the CDP-ethanolamine pathway, the CKI1 gene product was primarily responsible for phosphatidylcholine synthesis via the CDP-choline pathway. Unlike cki1Delta mutants, eki1Delta mutants did not suppress the essential function of Sec14p.
Amino Acid Sequence↗