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Home , Beta oxidation

Gluconeogenesis- continued 11/12/2014

Cori Cycle  Exchange of energetics between 2 different systems  Looks at a tissue for one reason or another takes pyruvate (end product of ) and makes lactate o Ex.: red blood cells (no mitochondria, can’t metabolize pyruvate), muscle cells under limiting conditions and lack of blood flow lactate build up o Need glucose more than the liver in each case o Lactate converts to pyruvate to OAA to PEP back to glucose in liver and glucose goes back to tissues in need  Exchange of high energy molecule for low energy molecule between the 2 systems (same with the cycle) Fructose overriding the signal in glucokinase regulation  Fructose goes to fructose 1-phosphate o Catalyzed by fructokinase  Fructose 1-phosphate then interferes with fructose 6-phosphate signal (which is a repressor of glucokinase)  Acts as effector, but not sure at which site Regulation of  Regulation of gluconeogenesis and glycolysis are interrelated (pretty much the same thing)  3 different chemical steps regulated that are unique to gluconeogenesis: o 1) Conversion of pyruvate to phosphoenolpyruvate by and phosphoenolpyruvate carboxykinase through oxaloacetate . acetyl CoA is a positive effector of this conversion . acetyl CoA is a negative effector of in pyruvate (not this pathway)  regulates conversion of pyruvate to acetyl CoA or OAA  determines fate of pyruvate o 2) Conversion of fructose 1,6-bisphosphate to fructose 6- phosphate by fructose 1,6-bisphosphatase . Effector control (reciprocal and simultaneous control over glycolysis and gluconeogenesis):  ratios of AMP and ATP  AMP is a negative effector of fructose 1,6- bisphosphatase and positive effector of glycolysis  ATP is a positive effector of fructose 1,6- bisphosphate conversion to fructose 6- phosphate by fructose 1,6-bisphosphatase  citrate determines how much material is available for biosynthesis  citrate is a positive effector for the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate by fructose 1,6- bisphosphatase  fructose 2,6-bisphosphate is a negative effector for the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate by fructose 1,6- bisphosphatase  phosphorylation/dephosphorylation of bifunctional controls the fructose 2,6-bisphosphate effector o Bifunctional enzyme signaled by glucagon to be phosphorylated by kinase a, which shifts metabolism towards gluconeogenesis . When the bifunctional enzyme is phosphorylated, it keeps the fructose 2,6-bisphosphate effector from repressing gluconeogenesis o Bifunctional enzyme signaled by to be dephosphorylated by phosphoprotein phosphatase, which shifts metabolism away from gluconeogenesis . When the bifunctional enzyme is dephosphorylated, it allows the fructose 2,6-bisphosphate effector to repress gluconeogenesis o 3) Conversion of glucose 6-phosphate to glucose by glucose 6-phosphatase . fructose 6-phosphate is a positive effector for the conversion of glucose 6-phosphate to glucose  This is just basic substrate availability control Hormone control of gluconeogenesis  3 metabolic components that are regulated universally by the same systems: o 1) . metabolism connection to gluconeogenesis: provides energy for liver to invest energy into oxidized molecules like lactate and reform glucose  Connection between lipids and o 2) Carbohydrates (like glucose) . glycolysis vs. gluconeogenesis . shift in oxidative catabolic pathway (glycolysis) vs. reductive anabolic pathway (gluconeogenesis)  controlled through same system o 3) Glycogen  glucagon & insulin o insulin signals to the liver that there’s high glucose levels . 1) Lipids  decreases fatty acid beta-oxidation  increases lipid synthesis . 2) Carbohydrates (like glucose)  increases glycolysis  decreases gluconeogenesis . 3) Glycogen  makes liver store more glycogen & stop burning glycogen . insulin activates phosphoprotein phosphatase and inactivates a  causes dephosphorylation of the bifunctional enzyme  promotes (storage of carbohydrates as glycogen)  Stops (liberation of glucose from glycogen)  Removes cAMP, so that the bifunctional enzyme cannot be derepressed (cAMP levels are decreased by the enzyme cAMP phosphodiesterase)  Activates the phosphoprotein phosphatase o glucagon tells liver there’s low [glucose] . 1) Carbohydrates (like glucose)  increases gluconeogenesis  stops glycolysis . 2) Lipids  increases oxidation of fatty acids  stops synthesis of fatty acids . 3) Glycogen  stops glycogenesis (storing carbohydrates as glycogen)  promotes liberation of glucose from glycogen to supply to blood (glycogenolysis) . Glucagon inactivates phosphoprotein phosphatase and activates protein kinase a  Causes phosphorylation of the bifunctional enzyme  Tissue differences: liver vs. muscle o liver metabolizes glycogen to send glucose out to the blood for tissues deficient in energy o muscle metabolizes glycogen to send glucose through glycolysis for carbohydrate energy to supply the muscle itself Transcriptional regulation of gluconeogenesis  Covalent modification requires the protein to already be there o This is a fast response, because we don’t have to go through the central dogma (transcription of the DNA, translation of the RNA, etc.)  Prolonged starvation and prolonged feast conditions are regulated differently (different from covalent modification and allosteric regulation) o Through transcriptional programming that controls the amounts of rather than inactivation/activation of those proteins o Slower response, but prolonged duration of modification  Signals aren’t on and off (glucagon/insulin), but ratios are shifted to shift metabolic responses o Receptors of cells perceive which signal as more dominant and then respond to it  Transcriptional level regulation response to Glucagon o Glucagon hits the 7 membrane protein pass receptor, the g- protein coupled receptor . This activates the g protein, which activates adenylate cyclase  This Makes cAMP  cAMP is a derepressor of protein kinase a o Increases protein kinase a, which sends a signal called cAMP response element binding protein (CREB) to proteins in the nucleus . CREB is activated when phosphorylated by protein kinase a . Once activated, CREB can bind to CRE (cAMP response element, which is a transcription factor)  Once CREB binds to CRE, it doesn’t increase transcription on its own, but is an activator that can pull in other co-activators to increase transcription of PEPCK gene  Basal components of transcription are still needed  PEPCK controls conversion of OAA to PEP  4 Functions of lipids o 1) Energy . fatty acids stored in adipose tissue as long-term energy than can then be liberated by fatty acid beta-oxidation to produce acetyl-CoA that can go through the TCA cycle and create energy for tissues, such as the liver during gluconeogenesis . Nonpolar neutral lipids are mostly used for long-term energy o 2) Insulation . Adipose tissue forms a layer beneath our skin that helps us trap heat and stay warm o 3) Membrane structure . Polar lipids are mostly used in cell membrane structures . is an example o 4) Signaling . IP3 and DAG  Inositol triphosphate signals calcium influx into the cell, which is an important positive effector of 1) phosphorylase kinase, 2) calmodulin-dependent protein kinase, and 3) protein kinase C  All of these kinases function to phosphorylate/inactivate glycogen synthase, which causes a metabolic shift away from glycogenesis and towards glycogenolysis  Phosphorylase kinase also phosphorylates/activates glycogen phosphorylase, which causes a shift towards glycogenolysis  Diacylglycerol signals protein kinase C to phosphorylate/inactivate glycogen synthase, causing a metabolic shift away from glycogenesis and towards glycogenolysis  Lipids are not easily definied, why? o No universal o Simply called lipids because they’re nonpolar (chemically physically similar) o Diverse collection of molecules . Not related in structure, function, or biosynthesis to one another  We are incapable of sustaining ourselves from fatty acid biosynthesis o We must consume dietary essential fatty acids . The 2 essential dietary fatty acids are:  1) linoleic  2) linolenic acid  These can be used to make arachadonic acid, which can be used to make important signaling molecules Structure and Chemistry of fatty acids and acylglycerols  Fatty acids are long hydrocarbon chains with a carboxyl group o Alkyl group = long hydrocarbon chain o Acyl group = long hydrocarbon/alkyl group with a carboxyl group attached . These are acyl lipids (carboxylic acid with a fatty acid as its R group) o Saturated means every in the alkyl portion of the acyl lipid is connected to either another carbon by a single bond and or completely surrounded by/“saturated” with hydrogen atoms o Unsaturated means you’ve removed some hydrogen’s and replaced them with double bonds between two . Double bonds between 2 carbons in a fatty acid are almost exclusively in the cis- configuration . Cis- means the hydrogen’s in the double bond are on the same side of the molecule, while trans- means they’re opposite  Typical fatty acids are even chain numbers o Most have 16 and 18 carbons (such as our 5 dominant ones)  Saturates and unsaturates o Saturated with hydrogens o Unsaturated have double bonds . Can have up to 6 double bonds typically . Mono- di- tri- etc. usaturates (depending on the # of double bonds)  Most unsaturated fatty acids are in the cis- configuration Nomenclature  Ene explains structural double bond position o Carboxyl end is the delta end (delta = triangle) . This is the typical way used to name fatty acids o Methyl end is the omega end (omega = w) . Sometimes more useful when naming fatty acid metabolites, because when we elongate a fatty acid chain, we do so from the delta end  So if we name the position of the double bond using the delta end, the position can change depending on elongation  If we name the position of the double bond using the omega end, however, the position will not change even if the fatty acid is elongated o Ex.: delta 9 means that 9 carbons starting from the delta end will be the location of the double bond in that particular fatty acid  Desaturases are that remove hydrogens from a saturated fatty acid to form a double bond, and thus, unsaturated fatty acid 5 dominant fatty acids  can exist in their base form with “ate” or acid form with “ic acid”  saturates (saturated with hydrogens) o FA means fatty acids o sFA means saturated fatty acids  unsaturates (contain a double bond) o Typical unsaturated fatty acids have between 1 and 6 double bonds and are classified as: . Monounsaturates or monoenes  abbreviated MUFA  mono unsaturated fatty acid . diunsaturates or dienes  2 double bonds . triunsaturates or trienes  3 double bonds . tetraunsaturates or tetraenes  4 double bonds  all of these can be abbreviated PUFA’s  poly unsaturated fatty acids . pentaunsaturates or pentaenes  5 double bonds . hexaunsaturates or hexaenes  6 double bonds  SCFA (9 and below carbons in the fatty acid chain) o Short chain fatty acids  MCFA (10-14 carbons in the fatty acid chain) o Medium chain fatty acids  LCFA (16-18 carbons in the fatty acid chain) o Long chain fatty acid o The 5 dominant fatty acids (palmitate, stearate, oleate, linoleate, and linolenate) are all LCFA’s  vLCFA (20+ carbons in the fatty acid chain) o very long chain fatty acids o less common in our cells o Include 2 main types: . 1) (20 carbons in the fatty acid chain)  Arachidonic acid is a type of :  Tetraenoic acid (contains 4 double bonds) o The double bonds are positioned at 5, 8, 11, and 14 relative to the carboxyl (delta) end  Gives rise to 2 important signaling molecules: o 1) (activate inflammation response to injury) o 2) (bronchiole constriction and anaphylactic response) . 2) docosanoids (signaling molecules made by oxidation of 22 carbon fatty acids)  The 5 dominant fatty acids:  1) common name: palmitate / o systematic name: hexadecanoic acid o saturated, because no enoic o short hand abbreviation 16:0 . first number is number of carbons in the fatty acid chain . 0 is the number of double bonds  2) common name: stearate / stearitic acid o systematic name: octadecanoic acid o short hand abbreviation: 18:0  3) common name: oleate / oleic acid o systematic name: cis-9-octadecaenoic acid . cis-9 tells us where the double bond is . enoic tells us there’s a double bond o short hand abbreviation: 18:1^delta9 . single double bond w/ designator . superscript delta 9 means the double bond is at the 9 position from delta  4) common name: linoleate / o systematic name: cis-9,12-octadecadienoic acid . dienoic tells us 2 double bonds o double bonds have to be methylene interrupted . if they’re not methylene interrupted, they’re conjugated, which provide very different chemical properties . all of our fatty acids are methylene interrupted, meaning there’s 2 carbons in between them o short hand abbreviation: 18:2^delta9,12  5) common name: linolenate / linolenic acid o systematic name: cis-9,12,15-octadecatrienoic acid . trienoic tells us 3 double bonds o short hand abbreviation: 18:3^delta9,12,15  Palmitic acid, oleic acid, and stearic acid are all made in our bodies  Linoleic and linolenic are essential dietary fatty acids o They can be referred to as omega 3 and omega 6’s, collectively Fatty acid structures  Pools of free fatty acids are kept in very low concentrations within the cell o They would disrupt cellular structures o So they exist, instead, as esters (alcohol plus an acid) . Typical esters of fatty acids (called acyl esters) include:  1) esters  3 hydroxyl group positions on glycerol that can accept a fatty acid  2 dominant acylglycerols (both neutral lipids): o 1) diacylglycerol (DAG) . important in membrane biosynthesis and long-term energy storage o 2) triacylglycerol (TAG) . important in long-term energy storage o monoacyglycerol is not common to our systems  2) Esters to a phosphopantothenic acid activated group  Either on a CoA or an ACP  Sources of fatty acids: o 1) de novo synthesis (of new) . occurs in the . FAS () . If the fatty acyl-CoA pools of the cytosol are increased, fatty acid beta-oxidation will be activated o If end products of fatty acid beta-oxidation build up, they can repress beta-oxidation o If acetyl-CoA isn’t utilized, this indicates the long-term energy is not needed and beta-oxidation will be repressed  Malonyl-CoA is a negative effector of CPT 1 (carnitate palmytic transferase isoform 1) o Malonyl-CoA (extender unit) is formed by Acetyl-CoA carboxylase (ACCase) . ACCase is involved in the beginning steps of fatty acid biosynthesis o Thus, a build up of malonyl-CoA will repress fatty acid beta- oxidation o ACCase converts acetyl-CoA to malonyl-CoA . ACCase is effector regulated by products of the biosynthesis pathway . ACCase is also feed forward regulated by citrate  Build up of citrate in the cell indicates it’s not being used  Citrate simultaneously effector regulates glycolysis . ACCase is covalently regulated by protein kinase a and phosphoprotein phosphatase  Ties back to and glucoagon/insulin signals  cAMP-depdendent phosphorylation inhibits ACCase  glucagon indicates low energy, thus, under low energy we don’t want to make fatty acids  insulin-dependent dephosphorylation promotes ACCase  insulin indicates high energy, thus, under high energy we want to make and store fatty acids  Adipose tissue is covalently regulated depending on fed or fasting state: o The lipases are sensitive to hormones . Glucagon activates lipase . Lipase liberates fatty acids . Fatty acids are brought to the adipose tissue, and ACCase is shut down . This depletes malonyl-CoA, which removes the inhibition of transport and activates beta-oxidation  Look at table 17.3 Metabolic regulation  Special separation (cytosolic vs. mitochondria) o Mechanism of regulation  Acyl group carrier (ACP vs. CoA) o Mechanism of lipid metabolism regulation  Utilization of reducing equivalents (NADPH vs. NADH or FADH2) o Mechanism of lipid metabolism regulation  Stereoisomeric form of D vs. L 3-hydroxyacyl-CoA o Mechanism of lipid metabolism regulation  Energy yields between systems o Don’t just write #’s, explain where the energy come from o Go over TCA cycle and electron transport system Additional mechanisms of fatty acid oxidation  Odd chain fatty acids o beta-oxidation occurs until we reach a 3 carbon proprionyl- CoA . Proprionyl-CoA is converted to succinyl-CoA that can then be used to make energy in the TCA cycle . Both beta-oxidation and the TCA cycle occur in the mitochondria  Unsaturated fatty acids o Beta-oxidation occurs until a double bound is encountered . Any double bound other than a trans-2-enoyl group (which is a double bond encountered in normal fatty acid beta-oxidation) will stop this system o Unsaturates have cis- double bounds that will not be processed normally under fatty acid beta-oxidation . 1) Enoyl-CoA isomerase will convert the cis-3 double bound to a trans-2 double bond  Beta-oxidation can also give rise to a conjugated double bond intermediate, which will stop the fatty acid beta-oxidation system  Double bonds are normally methylene interrupted . 2) 2,4-dienoyl-CoA reductase uses NADPH to convert the conjugated double bond system to a cis-3-enoyl-CoA methylene interrupted system  This is why unsaturated fatty acids yield less energy (they cost an NADPH) than saturated fatty acids under beta-oxidation  Additional NADPH is required . 3) Enoyl-CoA isomerase (again) isomerizes the cis-3- enoyl-CoA to form a trans-2-enoyl-CoA  Alpha-oxidation (deals with branched fatty acids) o We consume from plants . Beta-oxidation can’t deal with phytanic acid and must undergo alpha-oxidation o We clip off a single carbon from the branched molecule and lose it as CO2, we then reactivate to a CoA ester and continue until we hit another branch, at which point we would undergo alpha-oxidation again  Omega-oxidation o Through other reactions, we make 2 carboxyl ends on the fatty acid (this forms a dicarboxylate) o Esterifying one of these carboxyl ends with a CoA will eventually form succinyl coa (which is a dicarboxylate) . Succinyl-CoA then feeds into TCA cycle to form energy Bodies  are made from acetyl-CoA primarily in the liver o This is a mitochondrial localized system  This reaction requires: o 1) A distinct isoform of beta-ketothiolase . This enzyme is also used in mitochondrial fatty acid biosynthesis . And mitochondrial fatty acid beta-oxidation . Beta-ketothiolase condenses together 2 acetyl coA’s form acetoacetyl-CoA o 2) Hydroxymethylglutaryl-CoA synthase (HMG-CoA synthase) . Hydroxymethylglutaryl-CoA synthase adds another acetate from acetyl-CoA to acetoacetyl-CoA  This involves the consumption of a 3rd acetyl-CoA . Hydroxymethylglutaryl-CoA is also a central intermediate in cholesterol biosynthesis in the cytosol  Thus, the enzymes of this ketone body process have redundancy in isoforms o 3) Hydroxymethylglutaryl-CoA is acted on by a lyase that pulls back out a molecule of acetyl-CoA . Thus, with 3 acetyl-CoA’s consumed and 1 acetyl-CoA formed, there is a net consumption of 2 acetyl-CoA’s in this process (4 carbons) . Removing the CoA produces acetoacetate, which can be acted on by the beta-hydroxybutyrate dehydrogenase to form beta-hydroxybutyrate  Acetoacetate can also go through a spontaneous decarboxylation to from acetone  This process can be reversed in target tissue mitochondria to form acetyl CoA, which can enter the TCA cycle and be used for energy from ketone bodies in certain tissues o ATP citrate lyase transports acetyl-CoA to the cytosol to be used for fatty acid biosynthesis and cholesterol biosynthesis o Cholesterol is a 30 carbon molecule . Can be used to make testosterone, estrogen, cortisol etc. o HMG-CoA reductase is a drug target for drugs such as statin . This is the de novo pathway for producing cholesterol  Ketone body production regulation: o Regulated by availability of NADH . Ketone bodies are utilized for energy in the fasting state as a last resort for energy . In the target tissue, the dehydrogenase is reversed back to acetoacetate  Acetoacetate is then activated to a CoA  Using thiophorase, which exchanges the acetoacetate with a succinyl group forming acetoacetate-CoA