Bio98 Lecture 17 Regulation of fatty acids metabolism & degradation of amino acids

Where are the building blocks coming from?

-Malonyl-CoA: build from acetyl-CoA

-Both Malonyl-CoA & Acetyl-CoA are used in FA biosynthesis

-can break down FAs to make Acetyl-CoA; FUTILE CYCLE bc it’d waste all energy generated to rebuild them

-TCA Cycle is also a hub of biosynthesis (fats are createed and stored from other foods like sugar bc of the inhibition of siocitrate dehydrogenase)

• citrate → acetyl-CoA → FAs → Lipids

Understand the ways that FA metabolism is regulated

1) FA biosynthesis and oxidation are OPPOSING ACTIVITIES:

• when one is activated the other is inhibited (no futile cycle)

2) FA biosynthesis STORES energy, oxidation PRODUCES energy

3) Regulated by citrate and energy state (high/low ATP)

4) Regulated by transporters/compartmentalization

5) Regulated by hormones like insulin and glucagon

6) Regulated by enzyme phosphorylation state

Activation of FA biosynthesis

1) Phosphoprotein phosphatase 2A (PP2A) dephosphorylates the enzyme (citrate) → returns to active state

• stimulated by insulin signaling pathway (blood glucose = high)

2) Phosphorylation of ACC I by AMP kinase (AMPK) or protein kinase A (PKA) → ACC adopts less active state.

• PKA is stimulated by epinephrine and glucagon (blood glucose = low)

^^ Regulation of ACC (Acetyl-CoA carboxylase)

-activators: citrate, ATP, insulin

-inhibitors: palmitoyl CoA, AMP, glucagon

Regulation of FA oxidation via ?

transport control

• FA - CoA in cytoplasm

• FA - CoA in mitochondrion : degradation of FATTY ACYL-CoA

—> CARNITINE SHUTTLE involved

- INHIBITOR: malonyl-CoA
—> commits BIOSYNTHESIS not OXIDATION

- EXERCISE —> ACTIVATES oxidation
—> inhibits ACC from producing MALONYL-CoA
—> no MALONYL-CoA is there to inhibit FA transport for fat burning

Regulation of Lipase

- pancreatic enzyme that breaks down FATS into FATTY ACIDS + GLYCEROLS

- HORMONE SENSITIVE enzyme (lipase)
—> ACTIVATOR: glucagon
—> INHIBITOR: insulin

- EXERCISE also ACTIVATES this enzyme (lipase)

Understand different impacts of anerobic vs aerobic exercise

-Anaerobic: breakdown sugar (glycolysis), accumulate lactate.

Training: reduce fatigue and increase power burst (think back to the alligator)

-Aerobic: mostly burn fat, minor breakdown of sugar, produce CO2.

Training: reduce fatigue and increase endurance

Aerobic exercise training causes increases and decreases in?:

1) increase in hexokinase rate

2) Increase gluconeogenesis ability

3) Decrease in total LDH activity

• Purpose: to decrease lactate (causing soreness) formation

4) Increase the # and size og mitochondria; enhances:

• pyruvate dehydrogenase enzyme rate

• Krebs cycle enzyme rate

• Fatty acid Beta-oxidation enzyme rate

• Electron transport chain

5) Fatty acid availability for oxidation due to increased:

• lipase activity: increased uptake of fatty acids by skeletal muscle

• Acyl-CoA synthetase activity: increases activation of fatty acids for transport into mitochondria

• Carnitine transporter activity

Anaerobic training: it increases what and has little effect on what?

1) Increases anaerobic capacity

• more muscle cells to use more ATP

• increased glycolysis rate (raise PFK rate)

• increased gluconeogensis rate

• increase lactate tolerance in blood and muscle

• But has little effect on:

• Oxidative capacity (e.g. mitochondria number, burning fat, TCA cycle or ET)

• Cardiovascular adaptation (heart pumping rate)

Digestion: Stomach

-Enzymes are released as (1).

-Pepsinogen is activated by (2).

1) zymogens: an inactive form meant to prevent digestion of proteins within the cells making them

2) the low pH of the stomach to the active enzyme pepsin.

Digestion: secondary enzyme

-Other zymogens are activated by other enzymes.

ex. chymotrypsin is activated by trypsin

Methods of Amino Acid Digestion

1) Digested amino acids enter the blood stream in the intestine

—> can import SHORT POLYPEPTIDES or individual AAs into the intestinal wall
—> PEPTIDASE can break down the polypeptides into SINGLE AAs

2) Proteins can also be broken down inside cells + transported to blood

—> LYSOSOMES can digest proteins —> released into blood as SINGLE AAs
—> ENDOSOMES can ingest proteins —> released into blood as INTACT PROTEIN

targeted protein degradation

- need to RECYCLE proteins after they fulfilled their purpose

- need to DESTROY proteins if they are accumulating or aggregating or causing issues

ubiquitin

- small protein "tag" that COVALENTLY LINKS to a targeted protein that shows that PROTEIN NEEDS to be DEGRADED by a PROTEASOME

- gets popped off and REUSED

- repeated cycles lead to attachment of ADDITIONAL ones
—> POLYUBIQUITINYLATION (regulates protein levels)

proteasome

- protein DEGRADATION machine

- degrades any protein that has an ubiquitin "tag"

- MUTATION of this enzyme can cause: PARKINSON'S DISEASE, DEMENTIA, MISCARRIAGE

non-protein degradation tangent

- other tags that are similar to ubiquitin

- SUMO (small ubiquitin-like modifier)
—> regulates enzyme activity rather than destroying them
—> targeted proteins have ALTERED FUNCTIONS

- ISG15 (interferon stimulated gene of 15 kDa) is ANTIVIRAL
—> looks like 2 fused ubiquitin domains in 1 polypeptide chain

dietary amino acids

- can be used to MAKE proteins + be used to STORE energy for later

- organisms DO NOT have a way to store AAs for energy
—> use CARBOHYDRATES (glycogen) + LIPIDS (triaglycerols)

- AAs can be converted to things like α-keto acids BUT there is a BUILDUP of AMMONIA
—> amine can be lost as ammonia

α-keto acids

- AAs can be converted to this version by the enzyme TRANSAMINASE

- AMINE that is released can be converted to AMMONIA

- undergoes TCA cycle after NH4+ is released so that they can be further metabolized to produce ATP

glucose-alanine shuttle

- nitrogenous wastes generated in MUSCLE are transferred to PYRUVATE —> generates ALANINE
—> transamination of ANIMO ACID —> α-KETO ACID can occur between pyruvate and alanine

- ALANINE is transported from MUSCLE to LIVER through BLOOD

- alanine can undergo transamination + oxidative deanimation (cycle between α-ketoglutarate + glutamate)
—> AMMONIA (NH4+) is generated and is released as UREA

- pyruvate in the LIVER then undergoes GLUCONEOGENESIS

Urea cycle and how it is linked to the TCA cycle

- process in which excess ammonia (NH4+) that is released from dietary AAs is made into CARBONYL PHOSPHATE (high energy molecule) w/ carbamoyl phosphate synthetase; undergoes this cycle to make it into UREA (excreted)
- uses ATP
- primarily occurs in the LIVER CELLS

Urea Cycle Step 0. To produce carbamoyl phosphate, how many ATPs need to be spent?

2 ATP

Urea Cycle Step 1

- CARBAMOYL PHOSPHATE reacts with ORNITHINE (2 Ns; 21st AA) to form CITRULLINE (3 Ns)

- enzyme involved is ORNITHINE TRANSCARBAMOYLASE (OTC)

- happens in the MITOCHONDRIAL MATRIX —> transported to CYTOSOL

Urea Cycle Step 2

- CITRULLINE (in cytoplasm) reacts with ASPARATE to form ARGINOSUCCINATE (4 Ns)

- enzyme involved is ARGINOSUCCINATE SYNTHETASE

- ATP is needed (AMP + 2 Pi released)

- happens in the CYTOPLASM/CYTOSOL

Urea Cycle Step 3

FORMATION OF ARGININE

- ARGINOSUCCINATE turns into ARGININE (4 Ns)+ FUMARATE (side-product)

- enzyme involved is ARGINOSUCCINASE

- happens in the CYTOSOL

Urea Cycle Step 4

FINAL STEP: formatioln of urea & ornithine

- ARGININE turns into ORNITHINE + UREA (cycle completed)
—> urea goes through the blood into the kidneys —> released in URINE
—> ornithine feeds back into the 1st STEP

- enzyme involved is ARGINASE (+ H2O)

- happens in the CYTOSOL

How does the urea and TCA cycle connect?

Asp-Arginosuccinate shunt connect urea and TCA cycles

—> "communicates" between the two cycles
- transports malate (metabolite) into mitochondria

- TCA cycle in the mitochondrial matrix

- urea cycle in the cytosol

Example of TCA → AA degradation → Urea

Step #1: GLUTAMATE carries 1 NITROGEN
—> glutamate buildup can be TOXIC (ex. MSG) + needs to be broken down

Step #2: GLUTAMINE carries 2 NITROGENS
—> glutamate + ATP + NH4+ = GLUTAMINE
—> carried out by GLUTAMINE SYNTHETASE
—> NOT TOXIC but needs to be broken down

- GLUTAMINE ==> URINE
—> GLUTAMINE is transported through blood into the LIVER
—> GLUTAMINE is converted into GLUTAMATE + NH4+
—> carried out by GLUTAMINASE (liver and kidneys)

—> GLUTAMATE turns into α-KETOGLUTARATE + another NH4+ released
—> carried out by GLUTAMATE DEHYDROGENASE

—> NH4+ undergoes UREA CYCLE —> released in URINE

glucose-alanine cycle

- PYRUVATE is converted into ALANINE via ALANINE AMINOTRANSFERASE
—> GLUTAMATE transforms into α-KETOGLUTARATE

- ALANINE is then transported from MUSCLES to LIVER through the BLOOD

- ALANINE is converted back to PYRUVATE via ALANINE
—> α-KETOGLUTARATE is transformed into GLUTAMATE

- any EXCESS AMMONIA (NH4+) undergoes the UREA CYCLE

Oxidation of Selected Amino Acids: Same number of C as TCA

Alanine: ATA equals alpha-Kg & Glu = pyruvate

Serine: loss of H2O + serine dehydratase (PLP) + addition of H2O, out NH4+ = pyruvate

Defective A.A. oxidation leads to issues

Phenylketonuria (PKU): Lack ability to degrade phenylalanine

Albinism: Tyrosinase defect causes inability for melanin to be produced

Maple-syrup urine disease (MSUD): BCKDH defect; prevents B.C α-keto acid from undergoing TCA cycle

In total. To produce one Urea. How many ATPs need to be spent?

3