Enzymes Exam 3 Flashcards
Citrate Synthase
First enzyme of fatty acid synthesis in “phase I”, the transport of Acetyl CoA from Mito. to cytoplasm. Catalyzes condensation of Acetyl CoA with OAA to form citrate inside the mitochondria.
Citrate Lyase
Second enzyme of fatty acid synthesis in “phase I”. It converts citrate back into Acetyl CoA and OAA once it has entered the cytoplasm.
- Uses ATP, phosphorylation stimulates
- positively regulated by citrate and insulin (induces gene expression)
- negatively regulated by PUFA and Leptin
Malate Dehydrogenase
Reduces OAA to Malate still part of “phase I” of fatty acid synthesis.
- Occurs in the mitochondria after malate is transported in via malate-a-ketoglutarate transporter.
Malic Enzyme
- Converts cytosolic Malate to Pyruvate producing NADPH.
- Pyruvate then transported into the mitochondria via pyruvate transported .
- Fatty acid synthesis regeneration of OAA
Pyruvate Carboxylase
Turns pyruvate into OAA inside mitochondria Fatty acid synthesis regeneration of OAA
Acetyl CoA Carboxylase (ACC)
Rate limiting enzyme of Fatty Acid Synthesis, requires Biotin as a cofactor
- Uses ATP
- Induction of gene expression by high carb/low fat diet
- Allosteric regulation: + Citrate, - PUFA
- Hormonal regulation/phospho or dephospho: +insulin which activates PP1 to dephosphorylate, -glucagon/epi activates PKA to phosphorylate
- Active as a polymer and dephosphorylated
- inactive as a dimer and phosphorylated
- Function is to convert Acetyl CoA into Malonyl CoA
Fatty Acid Synthase
Enzyme composed of two identical dimers head to tail conformation 7 enzyme activities and an acyl carrier protein (ACP)
- Converts Malonyl CoA into Palmitate through 4 reactions repeated 7 times in the cytosol
- Requires 14 NADPH, each reduction (2 per cycle) uses 1 NADPH
- Positive regulation by insulin and glucocorticoids which increase synthesis of genes, also hig carb low fat diet increases synthesis
- Negative by PUFA to suppress synthesis, high fat and starvation lower synthesis
- Steps: Condensation of Acetyl CoA (on Cys-S) and Malonyl CoA (on Pan-S) and then reduction, dehydration, reduction repeat.
Fatty Acid Elongase
Synthesis of longer chain fatty acids which occurs in Ser or Mitochondria
- It lengthens the Fatty Acid by 2 carbon units at a time using NADPH
- SER uses Malonyl CoA as carbon donor
- Mito uses Acetyl CoA as carbon donor
Acyl CoA Desaturase
Introduces double bonds into the Fatty Acid occurs in SER using NAD(P)H and Oxygen
- Cant synthesize FA with double bonds beyond carbon 9&10
- introduce double bonds between 4-5, 5-6, 6-7, 9-10
What promotes synthesis of TAG’s in hepatocytes and adipose?
Excess carbohydrates in liver
Excess Carbs and fats in adipose
Hormone Sensitive Lipase
Enzyme in TAG degradation- occurs in post absorptive state-hunger/exercise!
IN ADIPOSE
- positively regulated by glucagon, epi, norepi which activate PKA phosphorylating perilipin allowing access to HSL to phosphorylate it
- negative regulation by insulin which dephosphorylates HSL making it inactive
- breaks down TAG into DAG releasing a free fatty acid for transport to liver to beta oxidation to make acetyl coa
ATGL,
LPL,
MAG
TAG degradation breaks TAG’s to DAG’s
DAG to MAG
MAG to glycerol and free FA
Fatty Acyl CoA Synthetase
Phase I of Fatty acid activation in preparation for Beta Oxidation
- on outer membrane of mitochondria reaction occurs in cyto
- forms thoester bond btw FA and CoA to make FA-CoA
- Outer mito mem permeable to FA-CoA not FA
Carnitine Palmitoyltransferase I (CPT 1 )
Phase I activation of Fatty acid for beta oxidation
- located in IMS
- Rate limiting enzyme in Fatty acid degradation-inhibited by Malonyl CoA
- Transfers Fatty Acyl from CoA to Carnitine making FA-Car
- moves FA-Car into IMS through CACT
CPT-II
Phase One of fatty acid activation final step before beta oxidation
- located in inner mitochondrial membrane
- Transfers Fatty Acyl from carnitine to CoA again
- Carnitine exits via CACT
- FA-CoA can enter matrix
Acyl CoA Dehydrogenase
First enzyme in Beta Oxidation does the first oxidation!
- Oxidation, hydration, oxidation, thyolysis
- FADH (=2 ATP) to CoQ ETC
- NADH (=3 ATP) to complex 1 ETC
- Acetyl CoA (=12 ATP) to TCA
- Repeat 7 times
- to tell how many times to do cycle: 26 carbon FA divide by 2 to tell how many acetyl coa present 13, subtract one bc last step gives two so 12 cycles for 26C
- 129 ATP used Net (used two with Fatty acyl coa synthetase)
Link Lipid and Carb oxidation
- Acetyl CoA from beta ox can go into TCA make citrate with OAA
- If low carbs there is low OAA so acetyl CoA isn’t utilized
- fasting or diabetes OAA conveted to glucose by gluconeogenesis
- Excess acetyl coa goes to ketone bodies
CAD:
Carbamoyl Phosphate Synthetase II
Aspartate Transcarbamoylase (ATCase)
Dihydrooorotase
Multifunctional eukaryotic protien for Pyrimidine De novo Ribonucleotide synthesis: Occurs in cytosol except for DHODH
- CPT II is a channel that adds amine from Gln to carbamic acid to make carbamoyl phosphate +reg by PRPP and ATP, -regulation by UTP
- ATCase activates (ATP) or inactivates (CTP) by changing conformation
- Dihydroorotase closes the ring-hydrolase in reverse
- Dihydroorotase Dehydrogenase occurs in mitohcondria
UMP Synthetase
Pyrimidne de novo ribonucleotide synthesis: cytoplasm, also multifunctional eukaryotic protien
- Removes pyrophosphate (PPi) when orotate is added to PRPP (orotate was from DHODH)
- Decarboxylates orotate to form uracil in syn conformation
- Hereditary Orotic Aciduria deficiency in UMP Synthetase
Nucleoside monophosphate kinase
Nucleoside Diphosphate Kinase
(Pyrimidine De novo synthesis ribonucleotides)
Two steps to create UTP from UMP
- Nucleoside Monophos. Kinasese are specific for each NMP it will transfer a phosphate from ATP to create NDP
- Nucleoside Diphos. Kinase are not specific one can act on all NDP’s. It will transfer another phosphate from a different NTP to create a NTP
- also does same thing with purines
CTP Synthetase
Last enzyme for pyrimidine de novo ribonucleotide synthesis
- CTP is the only nucleotide to be directly synthesized as a triphosphate it is activated by GTP and inhibitied by CTP
- Trades a carbonyl out on UTP for an amine from glutamine
Make IMP?
IMP is precursor for Purine de novo ribonucleotide synthesis
- Swap PPi on PRPP for amine from Gln
- Add Glycine
- Add formyl from N-10formyl THF complete 5 mem ring
- Add another amine from Gln to start second ring
- close 5 mem ring
- Add co2 from bicarb first to Gln then to the alpha C on gly
- Add Asp at carboxyl
- release Fumarate
- Add second formyl complete 6 mem ring
- Close forming hypoxanthine
Ribonucleotide Reductase
Converts ribonucleotides into deoxyribonucleotides using NADPH
- one enzyme for all NDP’s and NTP’s
- Catalytic Tyr free radical stabilized by Fe ions
- Specificity Site: allosteric site that is on off switch ATP promotes dATP inhibits
- Activity Site: allosteric site for volume control how much of what is made
dTTP Pathway?
Thymidylate Synthase?
Need to create dUMP:
- removal of PPi from dUTP or
- deamination of dCMP
Thymidylate Synthase adds methyl to dUMP to create dTMP
Dihydrofolate Reductase makes THF available for methyl donation without cant incorporate Thymine to DNA
What enzymes are used by primidines to interconvert between nucleobases and NMP’s in two steps?
- Phosphorylases (nucleotidases): nucleosides and nucleobases
- Kinases (nuclsoside kinase): nucleosides to nucleotides
- Thymidine Kinase 1 is in cytosol adds Phosphate to nucleoside to make nucleotide
- Nucleotidases convert nucleotides to nucleosides
What enzyme do purines use to intervoncert between nucleobases and NMP’s in one step?
Phosphoribosyltransferases
- Adenine Phosphoribosyltransferase makes AMP by taking adenine base and attaching it to PRPP to make AMP and remove PPi
- Hypoxanthine-Guanine Phosphoribosyltransferase makes IKMP/GMP
- guanine and PRPP to make GMP and release PPi
- Hypoxanthinie and PRPP to make IMP and release PPi
- HPRT deficiency is Lesch Nyhan Syndrome-purines cant be salvaged only degraded making uric acid -gout
Serine Dehydratase
Amino Acid Breakdown: A type of ammonia lyase that can directly deaminate Serine
- remove water and add water back to remove amonia
- Serine forms pyruvate
Threonine and Histide also have ammonia lyases
- Thr forms a-ketobutyrate
- Histidine forms trans-urocanic acid
AST/SGOT?
Catalyzes interconversion of Aspartate and Oxaloacetate
- in AA degradation: combine amino acid with a-KG to make glutamate and OAA
- in Urea cycle: OAA is converted to Aspartate by AST
- In synthesis: OAA to Aspartate by AST
- Similar to CPS II (which adds amine from gln to form carbamoyl phosphate
ALT/SGPT?
Aminotransferase that catalyzes interconversion of Alanine and Pyruvate
- In AA degradation: combind a-KG with alanine to form glutamate and pyruvate
- In AA synthesis: convert pyruvate to alanine
- In Urea ALT is used by muscle cells to safely transport NH4 to liver as alanine
Glutamate Dehydrogenase
Step two in AA degradation:
- Releases an ammonium ion which goes into urea cycle
- goes from Glutamate to a-KG again
Glutamine Synthetase
adds amine to Glu to make Gln
All cells besides muscle cells transport ammonia to liver via glutamine
- Glutaminase in the liver removes an amine from Gln to make Glu releasing NH4 again
CPS I
Committed step in the Urea Cycle
Occurs in the mitochondria!
- combines Co2 and NH3 to make carbamoyl phosphate using 2 ATP
- NAG is allosteric activator
- Similar to Glutamie Synthetase in AA metabolism
After Carbamoyl phosohate is formed in Urea cycle what happens?
- Ornithine is moved into mitochondria to combine with CP making Citrulline
- Citrulline is exported to cytoplasm and interacts with Asp which donates an amine (-2ATP) creating Arginine
- Whats left of Aspartate becomes fumarate
- Fumarate enters Mitochondria and goes to OAA and enters TCA
- OAA to Asp conversion by AST/SGOT
- Back to the arginine- ornitihine is made when urea is removed and ornitihine enters mitochondria to repeat the process.
- Addition of water when cleaving urea from Arg adds final oxygen to urea
Threonine can be converted to ___ two steps, releases Acetyl-CoA
Glycine (gly goes to Ser which can go to Pyruvate)
Glycine can be converted to ___.
Serine (serine goes to Pyruvate)
Serine can be directly deaminated to ___.
Pyruvate
Alanine and ___ exchanged by ALT/SGPT
Pyruvate
Cytosine is deaminated and desulfonated to form ___.
Asparagine deaminated to form __ and __.
NH4 and Asp
(aspartate is exchanged with OAA by AST)
Aspartate is converted between ___.
OAA by AST/SGOT
Proline, Arginine, and Histidine can all be converted to ___.
Glutamate
(glu can make a-KG)
Glutamine is deaminated to make ___
Glutamate
which goes to a-KG
Met, Val, Ile have carbon skeletons converted to ___
succinyl-CoA
Glutamine donates NH3 to ___ to form ___
Aspartate; Asparagine
