Molecular mechanisms of nutrient transport

Paracellular diffusion Water, some inorganic ions, and a lew other very small compounds can bypass the intestinal cells altogether by traveling (in either direction) through very narrow (4-XA) pores of the tight junctions sealing lite spaces between enterocytes. The tight junctions of the proximal small intestine consist of fewer strands of sealing proteins w ith pore sizes of about 8 A and are therefore more permeable than distal intestinal segments with tight junction pore sizes of only 4 A....

Taurine

I he ampholytic amino acid taurine (2-aminoethane sulfonic acid molecular weight 125) is a conditionally essential nutrient. Function Critical for kidney function and protection of cells against dehydration, eye and brain function, hormonal regulation, nutrient absorption (bile) and protection against oxygen free radicals (hypotaurine) Requirements In most people endogenous synthesis is adequate (dependent on cystein, niacin, vitamin B6. iron, and molybdenum). Prematurely born infants and...

Info

L-Phenylalanine (Phe, F) - Aromatic amino acids L-Lysine L-Arginine (Lys, K) (Arg, R> rigurr H.3 The most common ammo acids in proteins Protein amino acids Metabolic Tate Chemical isolcucinc arc another abundant source of amino groups for transamination in muscle, especially in the postprandial phase. All of these aminotransferases require pyridoxal 5-phosphate as a c ova lenity bound eofacior. Ammonium ions can also contribute directly to amino acid synthesis, but the ex ten I is limited....

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DihydrolipoamideN dehydrogenase (FAD) DihydrolipoamideN dehydrogenase (FAD) Glycine dehydrogenase, decartooxyiatin (TPP) Glycine dehydrogenase, decartooxyiatin (TPP) reabsorption the ioss of Gly into urine is minimal in healthy people. Losses into feces are negligible while gastrointestinal function is normal. Nitrogen from metabolized Gly is excreted into urine as urea or as uric acid. Nearly a quarter of the nitrogen in uric acid comes from Gly. Gly homeostasis is maintained through...

Minerals and trace elements

Iron Brain is critically dependent on adequate iron supplies, but threatened al the same time by the potential toxicity of excessive concentrations. Brain dysfunction in older people (e.g. Parkinson's disease) is often accompanied by iron accumulation in some brain regions, which may add to the damage. The BBB effectively separates brain iron metabolism from whole body iron metabolism and all proteins involved in iron metabolism are produced within the brain (Rouault. 2001). A tentative model...

1

1,2-Diacy(-sn-gtycerol phosphate H.,0 I,2-Diacyt-sn-giyce< wl Figure 6.19 Fat storage m water means thai it does not excrl osmotic pressure and is chemically quite inert. Adipocytes are specialized cells that arc able to store large amounts of fatty acids as triglyceride. Fatty acids in adipocytes and other tissues arc converted into acyl-CoA by several ligases specific for short-chain, medium-chain, and long-chain fatty acids as outlined above. Triglyceride synthesis occurs at the cvtosolic...

Transport and cellular uptake

Blood circulation- The main transport form in blood is pantothenate red blood cells contain pantothenate, pantetheine and 4'-phosphopantothenate. but little CoA (Annous and Song, IW5). lied cell membranes are normally impermeable for pantothenate, but infection with Plasmodium falciparum (malaria parasite) induces the opening of new permeation pathways to supply the parasite (Saliba el ul I998). C'oA does not cross cell membranes uptake into most tissues proceeds as pantothenate followed by...

Leucine

The hydrophobic neutral branched-chain amino acid I.-leucine (2-am i no-4-methyl- cooh valeric acid, alpha-aminoisocaproic acid. 2-amino-4-mcthylpentanoic acid, one-letter code L molecular weight 1311 contains I0,7u nitrogen. BCAA branched-chain amino acids CoA coenzyme A Flgur* 8.55 L-Leucmc HMGCoA hydroxymethylglutaryl-CoA Leu L-leucine LATI L-type amino acid transporter 1 (SLC7A5) LAT2 L-type amino acid transporter 2 (SLC7A8) Function The essential amino acid L-leucine (Leu) is needed for...

Metabolism

Thiamin can be phosphorylated to TPP in most tissues (Zhao, Gao, and Goldman, 20011 by thiamin pyrophosphokinase (EC2.7.6.2). This enzyme converts free thiamin and TMP to TPP and TTP In brain and other tissues a significant proportion of TPP is phosphorylated again to TTP by thiamin-diphosphate kinase (EC2.7.4. IS) in an ATP-dependent reaction. Some investigators (Shioda etal 1993) reported that adenosylatc kinase (EC2.7.4.3) facilitates transphosphorylation (TPP + A DP < -> AMP + TTP). but...

A A c AcvCVch

HaC CH C C N C c CH ' ' H, H, H H2 Hj CHa C S SH NH H2c CH C C N C c LH I Hj H, H H . Hi Flgurr 9,45 Upoamide is a covalently bound prosthetic group of pyruvate dehydrogenase and four other enzymes and 226. These lipoamides serve as acceptors for the acetyl residues from pyruvate, transfer them to acetyl-CoA. and reduce lipoamide to dihydrolipoamide in the process. Another component of ihe complex, dihydrolipoamide dehydrogenase (1 3 ECI.8.I.4) transfers the hydrogens ia FAD to NAD Ihe same...

Nikolas Kuehnic

JUJtUrtita UmhjMBl' lO-_ ---- HOOC g C C C COOH Figur* 8.4T Pathway* of L-lryptophan briakdown pattern. Alternatively, the PLP-dependent enzyme tryptophan aminotransferase (EC2.6.1.27) can deaminate Trp the fate of the resulting indole 3-pyruvate is uncertain, hut it may also undergo ring opening and rejoin the main catabolic pathway, Arylfor-mamidase (EC3.5.1.9) generates kynurenine by hydroly ing N-formy I kynurenine. Most kynurenine is then oxidized by the davoenzyme kynurenine...

Chlorophyllphytolphytanic acid

Chlorophyll is the green pigment that enables plants to capture light for photosynthesis. Chlorophyll consists of a porphyrin ring with magnesium and the phytol side chain. Phytanic acid is a phvtol metabolite. MFP2 peroxisomal multifunctional protein 2 SCPx peroxisomal protein sterol carrier protein X Function it lias been suggested that phytanic acid and other phytol metabolites specifically bind to RXR-likc receptors and participate in the regulation of the cell cycle. Food sources (ireen...

Using molecular databases

The vast amount of data on biological systems can make it hard to find a particular piece of information. The power of current Web-based systems helps to access data with great speed. The following describes some typical scenarios and pro ides directions to potential resources. How to get basic nutrient information Usually, a standard textbook (such as this one) will be the best starting point. I he American Society of Nutritional Sciences provides a website with brief outlines describing...

Nutritional summary

Function The diversity of flavonoids is loo great to assign them specific properties. It is particularly important to emphasize that many flavonoids arc extremely toxic for humans. However, various flavonoids in edible foods are likely to promote health through antioxidant effects, actions on cellular signaling events, binding to sexhormone receptors, and modulation of detoxifying enzymes. Ftavonoid-rich fruits and vegetables (but not necessarily pharmaceutical products) are likely to decrease...

Function

Energy fuel Eventually, most of the ingested Cys is broken down and its carbon skeleton converted into pyruvate (see above). The complete oxidation of Cys yields 4.312kcal g oxidation of CssC provides 4.093kcal g (May and Hill, 1990). Utilization of cither amino acid requires thiamin, riboflavin, niacin, vitamin 136. pantothenate. lipoate. ubiquinone, iron. inc. and magnesium disposal of the sulfur in Cys requires molybdenum. Protein synthesis Cys is a constituent of most proteins and peptides,...

Pyruvate

Pyruvate (pyruvic acid 2-oxopropanoic acid alpha-ketopropionic acid aeetylformic acid pyroracemic acid molecular weight 88) is a keUi-monocarboxylie acid. MCV1 proton monocarboxylic acid corransporter 1 (SIC16A1) MCT2 proton monocarboxylic acid corransporter 2 (5LC16A7) PLP pyridoxal S'-phosphace Function Pyruvate is ihe product of glucose. L-alanine, and L-scrinc breakdown. Food sources Insignificant amounts are present in foods from both animal and plant sources. In comparison, more than a...

What nutrients are

We depend for sustenance on what we consume, but fortunately we are not what we eat The foods that we eat and drink are broken down by grinding and digestion, sorted by selective absorption, and changed in metabolic reactions. The it It mate late of an absorbed compound in the body depends on how quickly it is metabolized for energy production or excreted with bile or urine. Most ingested compounds leave again after a short time-which is for the better. Some of those that insist on staying on...

Bromine

Bromine is a halogen (atomic weight 79.9) bromides (BrX) and bromates (Br(Oi)X) are its salts. Function Bromine I Br I is used by eosinophilic leukocytes for immune defense. Food sources Significant contributors to dietary intake grains, nuts, sea salt, seafood, and bread. Requirements. No requirements have been established. Intakes around X mg day appear to be adequate. Deficiency The consequences of chronically low intake are uncertain growth retardation and insomnia have been suggested....

Lipoate

Lipoatc (alpha-lipoic aetd thioctie acid obsolete names protogen. thiocytin. factor 11 or 11A, pyruvic oxidation factor molecular weight 2081 the oxidized form is water-soluble and the reduced form is fat-soluble. Function Lipoate is a co factor of several enzymes essential for fuel metabolism, it is a potent antioxidant and protects the liver and other organs against some toxins. Sources Endogenous synthesis and absorption of lipoate from bacterial production in the colon account for most...

Variation in smell sensitivity

The ability of individuals to delect low or any concentrations of particular odorants varies greatly between individuals and tends to decline w ith age. The inability to detect a particular odor, such as butylmercaptan Ithe overpowering foul odorant in skunk secretion), has been referred to as 'smell-blindness* (analogous to color blindness where sensitivity to one color is lost, but others arc still detected). Androstenone About 50 of people are not able to detect the odor ofandrostcnonc, even...

AAAnvW

Figur* 6.9 Chain elongation and desaturation These activities add in sum with each cycle a malonyl-CoA to the growing chain, oxidize two NADP1I molecules to NADP. and release one carbon dioxide molecule and a free coenzyme A molecule, Cham elongation The length of fatly acids with 12, 14 or 1 (i carbons can be extended in the cytosnl by the addition of 2-carbon units (Moon et ui. 2001). The first step is the conjugation to coenzyme A by long-chain-fatty-acid-C'oA ligase (EC6.2.1.3). A specific...

H[

Figure 7.8 Endogenous fructose synthesis In most Western societies the main source of Fru is the disaccharide sucrose Glc a-( 1 fS2) Fru which is a pervasive sweetener I hgh fructose corn syrup is a major source in the US, where it is added to many industrial food products including ketchup and bread. The Fru content in this syrup is increased by conversion of its Glc during industrial processing using glucose isomcrase D-xvlulose ketol-isomerase (EC5.3.1.S). Mixtures with equal amounts of...

Methionine

The polar neutral amino acid L-methionine (2-amino-4-(methylthioJbutyric acid, alpha-amino-gamma-methylmercaptobutyric acid, 2-amino-4-methylthiobutanoic acid gamma-methylthio-alpha-aminobutyric acid one-letter code M molecular weight 149) contains 9.4 nitrogen and 21.5 sulfur (one sulfhydry group). RDA recommended dietary allowance Function The essential amino acid L-methioninc (Met I is needed for the synthesis of proteins and is a precursor for L-cysteine (Cys). It has a special role as the...

Absorption of watersoluble vitamins

Ascorbate Ascorbic acid (vitamin C) is oxidized in the small intestinal lumen (possibly by ceruloplasmini and taken up as dehydroaseorbate via GLUT1 (SLC2AI). Once inside the cell, dehydroaseorbate is reduced again to ascorbate and transported into portal blood by a specific sodium-dependent ascorbate transporter. Thiamin Phosphorylated forms are cleaved by brush border alkaline phosphatase (EC3.I.3.1). the free thiamin can be taken up via the proton-ihiamin antiportcr (SLCI9A2), mainly from...

Absorption of phytochemicals

Flavonoids and isoflavones Absorption ranges from minimal to more than 30 between individual compounds. Uptake IS best if any attached sugars are remov ed by lactase or bacterial 0-glueosidases in the intestinal lumen. The ATP-binding cassette transporters MDRt (Hoffmeyereral 2000) and MRf'2 (Walgren era ., 2000) pump fiavonoid and isoflavonc conjugates across the apical enteroeyte membrane into the intestinal lumen. MRPI and several other transporters move conjugates across the basolateral...

Watersoluble vitamins and nonnutrients

539 Vitamin B6 -T , 581 634 MTHFR methylenetetrahydrofolate reductase (EC 1.5.1.20) MTR 5-methyl tetrahydrofolaie-homocysreine S-methyl transferase (EC2.1.1.13) Metabolism is an integrated system of reactions that cannot be viewed from the aspect of just one component such as a particular nutrient. Silencing of gene expression by DNA methylation. which depends on an adequate supply of S-adenosylmethione (SAM), provides an illustration of the interdependence of methionine, folate, riboflavin,...

Creatine

Creatine (N-(aminotminomethyI l-N-methy glycine, molecular weight 1311 is an ammo Function The phosphorylated form creatine phosphate provides an instantly available and vital source of energy in muscles and brain. Requirements Dietary intake is not necessary precursors are available from a balanced diet. 1 ligh intakes increase muscle and brain stores slightly and may provide a modest increase in short-term exercise performance. Food sources Present in significant amounts only in muscle...

Biopterin

Biopteritl (S-( R*,S*)-2-amino-6- 1,2-dihydoxypropy )-4( 111 )-ptcridmonc, 6.7-dihydropicridine, molecular weight 237) is a moderately water-soluble heterocyclic compound. The biologically active form is tetrahydtrobiopterin (BH4). BHt 6,7-dihydropteridine 8Hj 5,6,7,8-tetrahydrobiopterin FTP 6-pyruvoyltetra hydro pterin Function Biopterin is needed for the metabolism of phenylalanine, tyrosine, and tryptophan, and for the synthesis of hormones, neurotransmitters, and skin pigments...

Vitamin A

The term vitamin A usually refers to retino I vitamin Al, 3,7-di methy 1-9(2,6,6-trimethyl-I -cyclohexen-1 -yl)-2,4.6.8-nonatetraen-1 -ol, obsolete name ophthalamin molecular weight 2861, its esters, and the metabolically equivalent retinal (retinaldehyde. retinene, vitamin A aldehyde, axerophthal molecular weight 284). Beta-carotene, alpha-carotene. Figure 9.3 Several structurally related compounds have vitamin A activity cryptoxanthin, and a few other carotenotds, which can be metabolieally...

H00CvWAAA

Myristaic has one of the highest energy contents of any nutrient, prov iding about 9kcal g. Complete oxidation depends on riboflavin, niacin, pantothenic acid, carnitine, ubiquinone, iron and magnesium. Food sources Milk fat and other animal fats are especially rich sources, hut many solid plant fats also contain mvnstate. especially alter hydrogenation. Requirements Current recommendations suggest limiting total saturated fat intake to less than 10 of total energy intake. Deficiency...

The gastrointestinal tract

The various segments of the gastrointestinal tract cooperate to acquire and modify food, extract nutrients from it. and prepare the residue for excretion. This makes it elcar that the organs assisting in digestion, such as pancreas and liver, are as important as the intestines. Oral cavity and esophagus Solid foods are chewed which increases the surface area for digestion and facilitates mixing with saliva. Several glands (sublingual, submandibular. parotid, v on l-.bners and other glands)...

Central appetite regulation

Much of the activity related to appetite perception and intake regulation has been located to the arcuate nucleus of the hypothalamus near the third ventricle, the nearby ventromedial nucleus and lateral areas of the hypothalamus, increased expression of the oncogene c-fos in some of these brain regions correlates with appetite perception. NPY melanoeortin neurons Two types of neurons, w hich arc located mainly in the arcuate nucleus, constitute a significant portion of the appetite perception...

Potassium

Potassium kalium atomic weight 39.098 is an alkali metal with valence I. Two of the three naturally occurring isotopes. 39 93.22 and 41 6.77 . are stable isotope 40 0.012 is radioactive. ADH antidiuretic hormone Nutritional summary Function Potassium is the main cationie osmolyte within cells. The element plays a major role in body electricity maintenance of cellular polarity, neuronal signaling, heart impulse transmission, and muscle contraction , nutrient and metabolite transport, and enzyme...

Endogenous sources

Lnositol-3-phosphat synthase EC5-5.1.4 , an NAD-containing enzyme, catalyzes the internal cyclization of glucose-6-phosphate to inositol-3-phosphate. After removal of the phosphate group by myo-inositol-l or 4 -monophosphatase EC3.1.3.25 the free form is released into circulation. About 4 g myo-inositol per day is formed in the kidneys. Intestinal bacteria may also contribute to inositol supplies, but the amounts available from this source arc not know n. Myo-inositol-1 ord -monophosphate se V....