W9 Nitrogen Catabolism

Kreb’s Bicycle

The connected cycle that cycles malate and aspirate between the TCA and Urea

Amino Acids that Stimulate Glucagon Release

Ala, Cys, Met, Gly (G-CAM)

Released by AA catabolism***

Regulation of Urea Cycle

Urea cycle is stimulated by HIGH protein and regulated by Glucagon

Amino acid load is reduced by amino acid catabolism which increases OAA and alpha-KG levels for gluconeogenesis (gluconeogenesis → glucagon).

Regulation of CPS1

CPS1 is allosterically activated by N-acetylglutamate

N-Acetylglutamate is produced along with glutamate when AA catabolism is increased (feedforward mechanism)

N-acetylglutamate

Metabolite produced from glutamine GLU and Acetyl-CoA when AA catabolism is HIGH

• Acts as an allosteric regulator for CPS1

• ACTIVATES urea cycle

• Feedforward activator

(think F26BP but for urea cycle)

N-Acetylglutamate synthase (NAGs)

Enzyme that produces N-acetylglutamate from Glutamate and Acetyl-CoA

• Activated by Arginine

STIMULATE UREA SYNTHESIS (stimulate N-catabolsim)

Enzymes that Catalyze Ammonia Assimilation in Humans

1 Glutamate Dehydrogenase

2 Glutamine Synthetase

3 Carbamoyl-Phosphate Synthetase 1

4 Glycine Synthase

Stages of the Urea Cycle

0 Activation of Ammonia

1 Formation of Citrulline

2 Formation of Arginosuccinate

3 Formation of Arginine

4 Formation of Urea

Ammonia Toxicity

When high concentrations of ammonia result from the inability to assimilate ammonia

Ammonia dangerous as it crosses membrane barriers and blood brain barrier to ruin membrane potential

Hyperammonemia

Excessive concentrations of ammonia in blood/body

Different amounts in diff lifecycle due to diff ez capacity (highest in infants, lowest in adults)

Causes of hyperammonemia

1 Genetic differences in Urea cycle or NAGS

2 gastrointestinal bleeding

3 Drug therapeutics

4 High K+

Treatments for Urea Cycle Disorders (UCD)

Aromatic Benzoate and Phenylbutyrate

Treatments for N-Acetylglutamine Synthase (NADs) Disorders

Carbonyl glutamate

Carbonyl glutamate bypasses the need fot NADs to activate CPS1 for the Urea cycle by activating

Ornithine Transcarboxylase Deficiency

A urea cycle disorder that impairs OTC, ornithine transcarbomylase

Most common UTD

Deadly and Chronic (early in urea cycle)

Causes

• 1 Build up of Ammonia (→ CP can’t enter urea cycle)

• 2 Build up of Carbonyl-Phosphate (→ buildup of oleric acid)

Orodic Acidrea

Orodic Acid Buildup caused by accumulation of Carbonyl-Phosphate.

Is an intermediate in pyrmidine synthesis

Arginase Deficiency

UCD caused by impaired arginase synthase production

Last step in Urea cycle impairment → more mild/acute

Causes buildup of ARGININE

Harmful neurological impact

Reductive Amination

Reaction catalyzed By GLUTAMINE DEHYDROGENASE that adds N from Ammonia to alpha-ketoglutarate form Glutamate

• Requires NADPH (anabolic, requires E)

Glutamine Synthase

Ammination

TRAPS AMMONIA by converting GlutamATE to GlutAMINE

Anabolic, requires 2 ATP

Can be coupled with REDUCTIVE AMINATION to add 2NH4+ to Alpha-KG

• A-KG + NH4+ + NADPH → Glutamate + NH4+ + 2ATP* → Glutamate

Only occurs when cellular energy is HIGH

Importance of Glutamine

Glutamine transports Ammonia (carries 2 ammonia) AWAY from muscles and Brian

Main way to trap and transport NH4

Provides source of N for cellular biosynthesis

Treatments for UCD

aromatic acid benzoate

phenylbutarate

Treatment for Deficiencies in NAGs

Carbamoyl Glutamate

Double Filter System

Liver Acinus

Periportal Zone

Perivenous Zone

Glutamine Synthetase

Low capacity, High affinity for ammonnia

Fenestration

Ornithine Transcarboxylase Deficiency

UTD where a lack of OTD prevents enough conversion of ornithine to citrulline

Causes buildup of ammonia and carbamoyl phosphate

Arginase Deficiency

UTD where lack of arginine prevents adequate ammonia assimilation

Statins

Inhibit production of cholesterols and upregulate the cholesterol clearance genes

Chylomicron

Lipid transport molecule that is formed in the intestine and transports mostly TAGS to liver

• High TAG

• Low Protein

• Low Density

• Have APOCII protein

Very Low Density Lipoprotein (VLDL)

Lipid transport molecule that is formed in the LIVER and transports cholesterol, cholesterol esters, and TAGS out of the liver. Acquires APOCII and APOB100 in blood when it becomes metabolically active

• Higher cholesterol

• Empties itself of TAGS in blood

Low Density Lipoprotein

Lipid transport molecule that evolves form VLDL in the blood stream. Its ApoB100 receptors bind to cells and allows for their entry into cells through receptor mediated endocytosis.

• Lots of cholesterol and cholesterol esters

High Density Lipoprotein

Lipid transport molecule formed in the liver that transports cholesterols from tissues to the liver for clean up. Is a scavenging and reverse transport.

• Contains many cholesterol and protein molecules

• Contains ApoA-1 receptors

Also releases ApoCII and ApoE that bind to VLDL to make it metabolically active

ApoA-1

Apolipoproteins on HDL that activate LCAT. Esterifies with CHOLESTEROL to drive reverse cholesterol transport

ApoB100

Apolipoprotein on LDL and VLDL that bind to the LDL receptor on cells to mediate receptor-mediated endocytosis of the transportation molecules and allows cholesterol delivery into cells.

ApoC-II

Apolipoprotein on chylomicrons and VLDL that activates lipoprotein lyases that enable the release of TAGS into the bloodstream (triglyceride hydrolysis).

Steps in receptor mediated endocytosis

1 LDL binds to receptor through ApoB100 recognition

2 Receptor-mediated endocytosis occurs as the receptor and ligand enter the cell through endocytosis

3 Cholesterol esters, cholesterol, membrane lipids, and proteins are processed

Atheroslerosis

Disease that results when there is a problem with the receptor mediated endocytosis of LDL and excessive LDL circulation in the blood.

• Leads to inflammatory activation of monocytes that target cholesterol and LDL

• Leads to the formation of macrophages and foam cells

Foam Cells

Immune cells that have ingested excessive amounts of cholesterol or cholesterol esters, stimulated by an immune response to LDL inflammation

HMG-CoA reductase Activators

PPP (Phosphoprotein Phosphate) → dephosphorylates to activate

HMG-CoA reductase Represors

AMPK, PKA → Phosphorylate to repress

Oxidized Cholesterols or Oxysterols → feedback inhibition that initiates the Ez’s degradation

Essential Amino Acids

Thr, His, Ile, Lys, Met, Trp, Phe, Leu, Val

(THIK MWF LV)

(“THInK MWF LuV”)

Conditionally Essential Amino Acids

Gly, Gln, Ala, Cys, Try, Pro, Ser, Arg

Conditionally-esscential amino acids created from esscential amino acids

Cys (met) and Tyr (Phe)

Conditionally essential amino acids that may need to be consumed/used at higher quantities

Ala (need more at certain points in life)

Gln (need a lot in gnereral)

Gly (collagen)

Pro (connective tissue)

Sources of Amino Acids

1 Dietary intake

2 Protein Proteolysis

3 De novo synthesis

Scelenocystein

21st amino acid that’s made with the element selenium

• If present in enough concentration, AA synth continues past stop codon

• Helps maintain reducing environment in cells

  • involved in anti-oxidants (glutathione peroxidase)

Protein Turnover

Replacement of older proteins as they are broken down within the cell; breakdown of proteins to meet homolytic needs

Proteostasis

The constant process of protein synthesis and degradation; REGULATION of protein turnover that ensures misfolded, damaged, or aged proteins are removed

Mechanisms of Proteolysis

1 Ubiquination & Proteosome Degradation

2 Autophagic Pathway

3 Lysosome Degradation

Ubiquitination

The selective targeting of proteins for degradation in proteosomes by tagging them with ubiquitin. Added in a series of reactions involving 3 intermediate enzymes

Ubiquitin

Molecule covalent added to proteins for degradation tagging

Also involved in DNA repair, Cell signaling, Protein repair, and Protein Trafficking

(DC PrPt)

• HGHLY Selective

• Cytosol and Nucleus

• ATP-dep

Ubiquitination Enzymes

E1 Ubiquitin initiating enzyme

E2 Ubiquitination conjugation enzyme

E3 Ubiquitin protein lyase

Autophagy

the BULK degradation of cytoplasmic compartments; protein aggregates, organelles, and anything bulk in cytoplasm

• Requires E

• Fuels N metabolism

  • Cytoplasm → Autophagosome → Lysosome

Lysosome Degredation

The degradation of ENCLOSED PROTEIN, membrane protein, and long-lived intracellular materials

• Passive, does NOT require ATP

• helps degrade extracellular AA

Sequential Proteolysis

The continuation of the degrative process between the stomach and small intestine. Starts/initiated in the stomach and continues in the small intestine with bulk degradation.

Zymogens

Inactive or pro-enzymes that can be transported through different tissues safely before they are activated in their target tissue or at certain time.

• prevents self-degradation

Pepsin

Zymogen activated to pepsin in the stomach by low pH.

Initiates degradation of proteins.

Auto-cyclic activation; pepsinogen activates it

Released by pancreas

Trypsinogen

Zymogen activated to trypsin in small intestine/intestinal lumine

Amplifies degradation by acting as a CNETRAL ACTIVATOR for protease action

• Activates other zymogens like chymotrypsin → chymotrypsin

Released by pancreas

AA absorbtion Mechanism

Amino acids are absorbed by a mechanisms similar to glucose assimilation in the intestine

• AA enter lumine through 2ndary active transport w. Na+ symporter

• Aminopeptidases = transporters that allow AA entry into cell

• AA facilitated diffusion into bloods stream

• N+/K+ antiport

Peptide transporters

Transport di and tri peptides into intestinal cells

Amino Acid Oxidation

Process that occurs to break down (oxidize) amino acids when

1 There are excessive AA released from protein turnover (excessive amount)

2 #AA > body’s needs for AA (not needed)

3 Cellular proteins are used as fuel when carbohydrates are unavailable (use for fuel)

Transamination

The process of transferring an amino group

• removes an amino group form an AA and adds it to a keto-acid

• Keto-acid becomes and AA and AA becomes a keto-acid

Allows for AA and Nitrogen catabolism

Catalyzed by aminotransferases or transaminases

Pyridoxal Phosphate (PLP)

Essential cofactor and coenzyme form of VB6

In AMINOTRANSFERASES, receives amino group in E2 complex and is what holds onto the amino group in the enzyme

Converted to PMP as amino-carrying intermediate

Key aminotransferases

Ala aminotransferase (ALT)

Asp aminotransferase (ASP)

Ala aminotransferase (ALT)

Aminotransferase that converts Ala to PYR

Asp aminotransferase (ASP)

Aminotransferase that converts Asp to OAA

Cyclic amino acids UNABLE to undergo TRANSAMINATION

Proline and histidine; have secondary amino groups

Amino acids that CAN’T undergo TRANSAMINATION because of TOXIC biproducts

Threonine and Lysine have toxic byproduct when they’re transamainiated

Oxidative Deamination

The process of removing an AMINO group from an AA and to create Alpha-KG and ammonia for the purpose of NITROGEN CATABOLISM

• Reversable

• Makes NADPH (oxidative process)

• NH4+ formed enters Urea cycle

• in Liver’s MITOCHONDIRAL matrix

Glutamate dehydrogenase

Enzyme that catalyzes OXIDATIVE DEAMINATION

Removes hydrogen and to create NADPH

HIGHLY regulated

TransDeamination

The coupling of TRANSAMINATION and Ox-DEAMINATION to fully break-down or deaminate an AA fully

AA + keto-acid → Keto-Acid + Glutamate → (+H2O) → Alpha-KG + NH4+ (+NADPH)

Glutamate Dehydrogenase inhibition

GDH is inhibited under HIGH E conditions

• ATP, NADPH, GTP = inhibitors

Glutamate Dehydrogenase activation

GDH is activated under LOW E conditions

• ADP, GDP, NADP+ = activators

Deamination routs

1 Glutamine Dehydrogenase (Ox-deamination)

2 Glutaminase

3 Asparaginase

Glutaminase

MITOCHONDRIAL enzyme that deaminates GlutAMINE to GlutamATE

Important enzyme in removing brain ammonia

Wide dist.

Asparaginase

Enzyme that deaminates AsparagINE to AsprerATE

Helps remove Ammonia to urea cycle in brain*

Regulation of UREA cycle

Urea cycle is regulated by LEVEL OF PROTEIN or AMMONIA

• High protein = high urea cycle

• Only “on“ when needed

• Stimulated by GLUCAGON → stimulated by Ala, Gly, Met, and Cys release (G-CAM)

• Stimulated by AA CATABOLISM —> GLUCONEOGENEIS

CPS1 HIGLY regulated

CPSI is activated by N-acetylglucosamine in a feedforward mechanisim initiated by AA catabolism

Glucomic Amino Acids

Amino acids that can be converted to intermediates that can enter TCA/Gluconeogenesis

Ala (PYR)

Asp, Asn (OAA)

Gln, Glu (A-KG)

Q AND E (cue-andy → candy)

Ketogenic Amino Acids

Amino acids that can form intermediates that can be converted to KETONE BODIES

Leu, Lys

Ala, Ser, Cys, Gly (Potential Ketogenic)

“LiKe And SubsCriGe”

Ketogenic and Glucogenic Amino Acids

Amino Acids that can form intermediates ot enter TCS/Gluconeogenesis or form Ketone Bodies

Ile, Phe, Try, Trp, Thr

IF WYT (“if whit”)