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Amino Acid Serine - What is Serine and Its Functions?

N2 - During its intraerythrocytic life cycle, the malaria parasite Plasmodium falciparum undergoes dramatic metabolic and morphological changes and multiplies to produce up to 36 new daughter parasites. This rapid multiplication of the parasite requires an active synthesis of new membranes. The major component of these membranes, phosphatidylcholine, is synthesized via two metabolic routes, the CDP-choline pathway, which uses host choline as a precursor, and the plant-like serine decarboxylase-phosphoethanolamine methyltransferase (SDPM) pathway, which uses host serine as a precursor. Here we provide evidence indicating that the activity of the SDPM pathway is regulated by the CDP-choline precursor, choline. We show that the phosphoethanolamine methyltransferase, Pfpmt, a critical enzyme in the SDPM pathway, is down-regulated at the transcriptional level as well as targeted for degradation by the proteasome in the presence of choline. Transcript analysis revealed that PfPMT transcription is repressed by choline in a dose-dependent manner. Immunoblotting, pulse-chase experiments, and immunoprecipitation studies demonstrated that Pfpmt degradation occurs not only in wild-type but also in transgenic parasites constitutively expressing Pfpmt. The proteasome inhibitor bortezomib inhibited choline-mediated Pfpmt degradation. These data provide the first evidence for metabolite-mediated transcriptional and proteasomal regulation in Plasmodium and will set the stage for the use of this system for conditional gene and protein expression in this organism.

Phosphatidylserine can increase the availability of endogenous choline for de novo synthesis ..

Moughan . (1991) compared the determined growth of pigs fed a barley based grower diet with the response to lysine supplementation of a lysine deficient synthetic diet based on casein. The observed growth was 0.925 of the expected growth based on intake of apparently absorbed lysine. To achieve an equal ME intake, 15.3 percent more dry matter was fed of the test diet than the synthetic diets. Thus the endogenous losses would be less on the synthetic diet leaving more of the supplementary lysine available to support growth. The series of experiments by Batterham . (1990 - 1994) and Beech . (1991) all had the same form; a comparison of cottonseed meal, meat and bone meal and soybean meal as examples of feeds with low, medium and high ileal digestibility. The growth and N retention of pigs fed three diets formulated to supply the same limiting level of ileal lysine, methionine, threonine, tryptophan or isoleucine were measured. The main difference was observed between cottonseed meal and the other two meals, with smaller (lysine, threonine) and non significant differences (methionine, tryptophan), in N retention between meat and bone meal and soybean meal. Diets were fed on a scale to provide the same DE/W 0.75 but the cottonseed diets had 8.3 percent less DE/kg than the soybean diets, with the meat and bone meal diets intermediate. Consequently, the amount of dry matter fed differed and basal endogenous loss would be less for soybean than meat and bone meal or for cottonseed meal allowing more of the absorbed limiting amino acid to be used for growth. The presence of gossypol and raffinose in cottonseed makes this protein particularly susceptible to heat damage by binding, specifically with the epsilon-amino group of lysine (Martinez ., 1961). This may make it unavailable without any major change in digestibility of the protein (see below). Cottonseed meal and products such as dried milk powders where reducing sugars are potentially present, may be special cases where ileal digestibility fails to reflect the full loss of available lysine through early Maillard reactions. For the majority of protein concentrates this is unlikely to be a major factor. Indeed, the Batterham group in a study of isoleucine, where the meals used were cottonseed, lupin seed meal and soya bean meal, ileal digestibility correctly predicted growth performance (Batterham and Andersen, 1994). Correction for the known differences in ileal true digestibility must be an improvement over the use of chemically determined total amino acid content.

Metabolism – Proteins | Biochemistry for Medics – …

Alternatively, homocysteine unit c - famate met- cysteinr FIG.1.-Proposed pathway of choline synthesis.

demonstrated that nearly allphosphatidylserine and a minimum of 70% of phosphatidylethanolamine is on theinside surface of the human erythrocyte membrane, thus "presenting a strongevidence for an asymmetric arrangement of phospholipids" ().

First demonstration of an inhibition of sterol biosynthesis (HMG-CoA reductaseactivity) by oxygenated derivatives of cholesterol in cultured mammalian cells ().

For the first time, the existence of polyunsaturated fatty acids was reported inmarine bacteria ().

29-70).

The first component protein of an enzyme of fatty acid biosynthesis, fatty acidsynthase, was purified ().

Polyprenol diphosphates were shown to be involved in the biosynthesis ofpolysaccharides in () and in the biosynthesis of peptidoglycans in ().

The structure of juvenile hormone of insects was elucidated by Roller H ().

Vitamin B6 | Linus Pauling Institute | Oregon State …

The first step in choline biosynthesis is the direct decarboxylation of serine to ..

N2 - In Saccharomyces cerevisiae, the three-carbon of serine is normally the major one-carbon donor, although glycine and formate can substitute for serine. The second carbon of glycine enters via the glycine cleavage system in the mitochondria and can satisfy all cellular one-carbon requirements. It remains unresolved, however, as to the route by which these mitochondrial one-carbon units supply cytosolic anabolic processes. In the present work, we have used yeast mutants blocked at selected sites and 13C NMR to trace the incorporation of glycine-derived mitochondrial 5,10-methylenetetrahydrofolate into nonmitochondrial synthesis of choline and purines. Label incorporation into choline traces the methylation pathway of choline synthesis from production of serine to methylation of phosphatidylethanolamine. The active one-carbon unit of S-adenosylmethionine involved in methylation reactions originates almost solely from C3 of serine. On the other hand, flow of mitochondrial one-carbon units to 10-formyltetrahydrofolate for purine synthesis is shown to occur via both serine and formate. Formate transport accounts for at least 25% of the total, even during growth with sufficient serine to provide for the one-carbon requirements of the cell. This work shows that the synthetase function of the cytosolic C1-tetrahydrofolate synthase plays a critical role in the processing of mitochondrial one-carbon units to 10-formyltetrahydrofolate pools. In addition, this study provides evidence of two pools of glycine within the mitochondria and establishes a system of analyzing flux into the different folate derivatives.

AB - In Saccharomyces cerevisiae, the three-carbon of serine is normally the major one-carbon donor, although glycine and formate can substitute for serine. The second carbon of glycine enters via the glycine cleavage system in the mitochondria and can satisfy all cellular one-carbon requirements. It remains unresolved, however, as to the route by which these mitochondrial one-carbon units supply cytosolic anabolic processes. In the present work, we have used yeast mutants blocked at selected sites and 13C NMR to trace the incorporation of glycine-derived mitochondrial 5,10-methylenetetrahydrofolate into nonmitochondrial synthesis of choline and purines. Label incorporation into choline traces the methylation pathway of choline synthesis from production of serine to methylation of phosphatidylethanolamine. The active one-carbon unit of S-adenosylmethionine involved in methylation reactions originates almost solely from C3 of serine. On the other hand, flow of mitochondrial one-carbon units to 10-formyltetrahydrofolate for purine synthesis is shown to occur via both serine and formate. Formate transport accounts for at least 25% of the total, even during growth with sufficient serine to provide for the one-carbon requirements of the cell. This work shows that the synthetase function of the cytosolic C1-tetrahydrofolate synthase plays a critical role in the processing of mitochondrial one-carbon units to 10-formyltetrahydrofolate pools. In addition, this study provides evidence of two pools of glycine within the mitochondria and establishes a system of analyzing flux into the different folate derivatives.

Figure 20-26 The pathway for phosphatidylcholine synthesis from choline in mammals ..
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Disease Prevention Immune dysfunction

Protein synthesis in the body involves a considerable expenditure of energy to create the activated amino acids to be linked together. In addition, protein tissues are constantly being turned over. For every one unit of net accretion of protein about 5 units of protein are synthesised. Some tissues are turning over faster than others. Indeed some of the fastest tissue replacement, such as in the intestinal epithelium and liver, lead to little or no net accretion. The energy cost of protein synthesis in protein turnover, just to maintain the existing protein, has been estimated to account for 15 to 33 percent of energy needed for maintenance. When additional energy is provided, there is an increase in protein synthesis and a decrease in protein degradation and these two effects combine to enhance net protein retention. When additional protein is supplied at constant energy, there is an increase in both protein synthesis and in protein degradation, resulting in a smaller net increment in protein retention. This is illustrated in Figure 5, which gives the determined synthesis and degradation contributions to the net N retention. With increasing protein in the diet there are frequently small improvements in carcase quality, measured as increased protein and decreased fat content. These changes arise from the decreased net energy value of protein compared with carbohydrate and the increased energy required for increased protein turnover driven by higher dietary protein intake, resulting in reduced energy available for fat synthesis.

Creatine Supplement - Unbiased Review on Usage, …

Figure 5. The effect on protein synthesis, degradation and net retention in pigs when fed a basal diet supplemented with either fat or carbohydrate at a constant protein level, or with protein supplied at constant energy. Source: Reeds ., 1981

Icon Isotopes : Carbon-13 Compounds

Dietary protein is not used efficiently as a source of energy. Although the gross energy of protein is greater than that of carbohydrate (23.6 kJ/g v 17.4 kJ/g for starch), when protein is used as an energy source the N has to be excreted as ammonia (fish), urea (mammals) or uric acid (birds). The ME value of protein at zero N retention takes into account the loss of energy in the excreta, such that the ME of protein and carbohydrate are approximately similar. The ME value for mammals and birds, however, does not take into account the energy costs of synthesising urea or uric acid and the cost of excretion in the kidney. Net energy (NE) of the diet represents the useful energy used to replace the losses of maintenance and the net deposition of energy as new tissue in growth or milk secretion during lactation, after subtracting the heat losses of metabolism.

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