Tca Cycle And Oxidative Phosphorylation

1. Matrix: all TCA cycle rxns occur within

-within IM

2. OM: permeable to many cmpds b/c has pores

3. IM: impermeable to everything (including H+, some H2O and gases may slip through) → specific carriers transport molecules across it

-foldings = cristae

*source of E for the cell via oxidative phosphorylation

***CO2:

1. isocitrate dehydrogenase

2. α -ketoglutarate dehydrogenase

(PDH)

NADH:

1. isocitrate dehydrogenase

2. α -KGDH

3. malateDH

(PDH)

FADH2:

succinate DH

GTP:

succinyl-CoA synthetase

*

Carbs: enter as Acetyl-CoA

FA: oxidation → Acetyl-CoA

aa degradation: → TCA intermediates for gluconeogenesis or E production:

1. α -ketoglutarate

2. succinyl-CoA

3. fumarate

4. OAA

*

*

*

*

*

*

Central point of metabolism:

1. Generate E by oxidizing acetyl-CoA to CO2 and H2O

-- e- must be removed from the 2 Cs → accepted by NADH (6) and FADH2 (2)

--acetyl-CoA is produced from pyruvate, FA ox, aa ox

2. Supply biochemical intermediates for:

a. heme synthesis

b. aa synthesis

3. Entry point for carbs, FAs, aas

maltose, sucrose, lactose in the stool

Fructose

(reducing sugars have a carbonyl)

Adipose/muscle

8 e-

(2Cs x 4e-)

Thermodynamics

amount of E required/released by a rxn → Gibbs Free E

Δ G= Δ H - T Δ S

Δ H = change in enthalpy

Δ S = change in entropy

Δ G = (-) → rxn proceeds in forward direction

Free E change of a rxn under standard conditions:

298 K = 25 oC

1 atm P

all reactants and products at initial conc = 1.0 M

Biochemical Standard of Gibbs Free E

Free E chnage at:

pH = 7.0

H2O= 55.5 M

all other reactants and products at initial conc. = 1.0M

(result of water not being able to be 1.0 M and the effect pH has on bio rxns)

A+B → C+D

Δ G =Δ G^o' + RTln [C][D]/[A][B]

factors for when aren't under standard conds.

R= 1.987 cal/mol-K (gas constant)

T=kelvin

Δ G (-) → rxn proceeds

(look up Δ G^o' in a table)

can be added together

4.18 kJ = 1 kcal

small product/reactant ratio → (-) RTln

(is created in cytoplasm→ must be transported in)

-crosses through pores of OM

-two transporters in IM:

1. Symport: (2o active transport)

-protons simultaneously pumped in down their conc grad w/ pyruvate

2. Antiport:

-citrate (3 neg. charges) out, pyruvate (1 - charge) in

-also driven by proton gradient (electrical grad)

1. lactate

2. alanine

in mito:

3. OAA

4. Acetyl-CoA → can no longer be used to make glucose

*why FAs can't be used to make glucose

Pyruvate + CoA + NAD+ → Acetyl-CoA + CO2 + NADH + H+

-oxidative decarboxylation= substrate is α -ketoacid

-enzyme has five subunits*

2 regulatory

3 catalytic:

1. pyruvate decarboxylase (E1): binds thiamin pyrophasphate (B1)

2. Transacetylase (E2): utilizes lipoic acid

3. Dihydrolipoyl dehydrogenase (E3): has bound FAD, **shared w/ other enzymes that perform oxidation decarboxylation rxns (E3 mutation affects all of these)

1. Thiamine (B1) → Thiamin pyrophosphate

2. lipoic acid

3. FAD

4. coenzyme A

-derived from thiamine (B1) via phosphorylation (ATP → AMP) adding two P groups on

- Thiazolium ring has acidic H that is easily lost → helps break C-C bonds of two structure types:

1. α - ketoacids (bw/n two carbonyls)

2. carbohydrates (bw/n carbonyl C and α C connected to hydroxy)

flavin - D- Ribitol - pyrophosphate - D-Ribose - Adenine

(flavin-ribitol-ADP)

-ribitol (reduced ribose) and flavin derived from riboflavin (B2)

-stronger oxidizing agent than NAD+ → FADH2 is a weaker reducing agent than NADH

-1 e- + H+ at a time (vs. hydride transfer = two at a time in NAD)

-derived from pantothenic acid (phosphopantothene)

-provides active sulfhydryl to conserve E in a thioester linkage in pyruvate dehydrogenase rxn

-five-membered ring w/ disulfide bond

-pyruvate dehydrogenase rxn:

--disulfide reduced then oxidized

interferes w/ cmpds containing adjacent sulfhydryl groups :

-lipoic acid → pyruvate dehydrogenase, α -ketoglutarate DH

once acetyl-CoA is formed, it cannot be used to produce glucose

catalyze oxidation decarboxylations

1. TCA:

-a. pyruvate dehydrogenase

-b. Isocitrate dehydrogenase?????

-c. α -ketoglutarate dehydrogenase

2. branched-chain aa metabolism

3. α - ketobutyrate → propionyl-CoA

*mutations in this subunit affect all of these rxns

1. lactic acidemia

2. neuro probs (brain dependent on glucose)

-X-linked dom: E1 α subunit located on X-chrom → most common defect

1. Beriberi- alcoholism, malabsorption (alcohol blocks thiamin (B1) uptake from gut)

*individuals usually get one or the other, don't know what determines which

a. Dry

b. Wet

2. Wernicke-Korsakoff Syndrome- brain disorder, lack of thiamin

a. Wernicke encephalopathy

b. Korsakoff syndrome

affects NS:

1. difficulty walking

2. loss of feeling in hands and feet

3. mental confusion/speech difficulties

4. Nystagmus

5. tingling

6. vomiting

(7. coma

8. death)

cardiovascular system:

1. awakening at night short of breath

2. increased heart rate

3. shortness of breath w/ activity

4. swelling of lower legs

5. can lead to congestive heart failure

-result of beriberi going on for too long

-symptoms may be reversed if given thiamine

1. confusion, loss of mental activity (→ coma, death)

2. loss of mm. coordination, leg tremors

3. Nystagmus, double vision, eyelid droop

4. alcohol w/drawal symptoms

-evolves from Wernicke encephalopathy

-not usually reversible

1. inability to form new memories

2. loss of memory

3. confabulation (making up stories)

4. hallucinations

vitamin C

1. Citrate Synthase

2. Aconitase

3. Isocitrate dehydrogenase

4. α -ketoglutarate dehydrogenase

5. Succinyl-CoA synthetase

6. Succinate Dehydrogenase

7. Fumarase

8. Malate dehydrogenase

Acetyl-CoA + Enz-B: → nuc-Acetyl-CoA

nuc-Acetyl-CoA + OAA → Citroyl-CoA → Citrate + HSCoA

-Citroyl-CoA:

--not found in soln, only bound to enzyme

--high E thioester → hydrolysis makes rxn favorable

Δ G = -8 kcal/mol,

Not reversible→ OAA levels stay low

citrate ↔ (H2O out) + Cis-Aconitate (H2O in) ↔ Isocitrate

Citrate:

-symmetrical

-aconitase treats dehydrates and rehydrates asymmetrically→ always the same bond

Δ G^o' = (+)

ONLY TCA rxn positive under cellular conds

90:6:4 ratio, rapid utilization of isocitrate allows rxn to proceed

isocitrate + Enz-B: + NAD+ → NADH + oxalosuccinate → CO2 + α -ketoglutarate

-oxidation-decarboxylation

-very different rxn mechanism from pyruvate dehydrogenase

-use E3??

Δ G^o' = -5 kcal/mole → helps drive aconitase rxn

α -KG + NAD+ + CoA → Succinyl-CoA + NADH + CO2

-oxidative decarboxylation

-uses E3 (same cofactors as PDH!)

Δ G^o' = -8 kcal/mole

Succinyl-CoA + Pi + GDP ↔ succinate + GTP + CoA

-Pi displaces CoA → high E bond → substrate level phosphorylation

-Δ G^o' = -0.8 kcal/mole → easily reversible

GTP + ADP ↔ GDP + ATP

AcCoA + OAA + 2NAD+ + GDP + Pi + CoA → succinate + 2CO2 + 2NADH + GTP + 2CoA

-2 carbons have been lost

-4 e- have been lost

- 1 GTP (→ ATP) has been gained

succinate + FAD ↔ fumarate + FADH2

-oxidation of C-C bond → requires strong oxidizing agent = FAD

**enzyme is attached and embedded within inner mito membrane=not found in matrix

fumarate + H2O ↔ Malate

(hydroxyl group replaces c=c bond in fumarate)

malate + NAD+ ↔ OAA + NADH

Δ G^o' = 29.7 kJ/mol

-cellular conds: low intramito [OAA] from high activity of citrate synthase and use of OAA for gluconeogenesis

aconitase

citrate ↔ (H2O out) + Cis-Aconitate (H2O in) ↔ Isocitrate

aconitase (+6.3 kJ/mole)

Malate dehydrogenase (+29.7 kJ/mole)

-57.3 kJ/mole

Acetyl CoA + 2H2O +3NAD+ + FAD + GDP + Pi → 2CO2 + 3NADH + 3H+ + FADH2 + CoA + GTP

10 moles high E bonds: (9 ATP, 1 GTP)

3 NADH x 2.5 ATP = 7.5

1 FADH2 x 1.5 ATP = 1.5

1 GTP

32 ATP (OR 30)

same for glu and gal

16 x

BUT glycolysis much faster → mm. use glycolysis when exercising

PDH (which isn't actually in cycle)

Inhibitors:

Allosteric: (via products)

1. acetyl-coA (competive inhibitor of CoA)

2. NADH (competive inhibitor of NAD+)

Covalent:

3. phosphorylation by PDH kinase → PDH-b

Activators:

1. PDH phosphatase → PDH-a

2. (CoA, NAD+, Ca2+)

PDH-a + ATP → PDH-b + ADP

-phosphorylates pyruvate decarboxylase (E1) subunit at 3 Ser

-distinct from cAMP dependent protein kinase (location= mito vs. cyto)

Activators: (same as allosteric inhibitors of PDH)

1. NADH

2. Acetyl-CoA

Inhibitors:

1. Pyruvate

2. ADP

PDH-a: active, not phsophorylated

PDH-b: inactive, phosphorylated

PDH-b + H2O → PDH-a + Pi

Activators:

1. Ca2+

2. Insulin

liver pyruvate kinase

1. Pyruvate DH**

2. Citrate Synthase

3. Isocitrate dehydrogenase

4. α -ketoglutarate dehydrogenase

8. Malate dehydrogenase

*NADH is key player → enzymes that produce NADH will be inhibited by it

inhibited by citrate

Activators:

ADP

Ca2+

Inhibitors:

NADH

**regulated so that citrate can accummulate b/c aconitase favors citrate formation→ signifies adequate building blocks → transported to cyto and inhibits PFK-1 (slowing glycolysis) and activates FA synthesis (citrate is substrate for FA production)

Activators: Ca2+

Inhibitors: NADH

**regulated b/c can form glutamate in one step → leaves cycle; encouraged if excess E is present

inhibited by NADH

disrupts TCA cycle:

competitive inhibitor of succinate DH

(similar structure to succinate minus 1 methylene)

disrupts TCA cycle:

disrupts enzymes requiring lipoic acid:

1. PDH

2. α-ketoglutarate DH

disrupts TCA cycle:

produces fluorocitrate → blocks aconitase

disrupts TCA cycle:

NADH accummulates in mito → NADH producing enzymes inhibited

disrupts TCA cycle:

NADH accumulates → NADH producing enzymes inhibited

1. cholesterol synthesis

2. FA synthesis

3. oxidation for E

CANNOT be used as a precursor to gluconeogenesis

-requires it to become pyruvate or OAA

-PDH is irreversible

-is 2 Cs → condenses w/ OAA → 2Cs lost as CO2 → no net synthesis of OAA only its regeneration

-no mammalian pathwyas for production of OAA from 2 acetyl-CoA b/c we are missing two enzymes necessary

--glycoxylate cycle in plants and bacteria can do this

OAA:

OAA + AcCoA → citrate (very favorable)

OAA + NADH → malate + NAD+ (favorable direction)

these two rns redice OAA levels w/n TCA cycle → OAA stays at low levels → keeps malate dehydrogenase favorable under cellular conds

→ Anaplerotic rxns replenish OAA so cycle can continue

citrate → fatty acids, sterols

α -ketoglutarate ↔ glutamate → other aas, purines

succinyl-CoA → Heme, Chlorophyll

Malic Enzyme: malate ↔ pyruvate

OAA ↔ Aspartate → other aas, purines, pyrimidines

-refilling rxns for TCA cycle

1. OAA*** (major one via pyruvate)

2. Acetyl-CoA

3. α -ketoglutarate

4. succinyl CoA

5. Fumarate

glycolyisis → pyruvate → OAA via pyruvate carboxylase

Transaminations from aas:

alanine → pyruvate → OAA (via pyruvate carboxylase)

aspartate → OAA

Carbs, FAs, aas → Acetyl-CoA

aas → glutamate → α -ketoglutarate via:

1. transamination rxn

2. glutamate dehydrogenase (NAD+ in, NADH and NH4+ out)

Valine, Isoleucine → propionyl CoA → Succinyl-CoA

Odd chain FAs→ propionyl CoA → Succinyl-CoA

aas → fumarate

high E levels (increased NADH) → isocitrate DH inhibited → citrate accumulation → citrate leaves mito → PFK-1 inhibited → E storage begins (fat and glycogen synthesis)

reciprocal:

high [Acetyl-CoA]: PDH inhbited, pyruvate decarboxylase activated → more OAA produced →

1. condenses w/ excess acetyl-CoA for FA synthesis (high BG) OR

2. used for gluconeogenesis (low BG)

(depends on cell's needs)

α -ketoglutarate

succinyl-CoA synthetase

(inhibits free Pi rxns)

citrate synthase???????????***********

-generate E as ATP from e- flow:

--e- flow from reducing agent (NADH, FADH2) → more stable carrier (O2 → H2O)

--as e- flow to most stable form E is released and captured as a proton gradient

--proton flow down electrochemical gradient drives ATP synthesis (E captured w/n high E bonds of ATP) = hemiosmotic hypothesis (theory)

e- flow pumps H+ from mito matrix across IM to intermembrane space

Nernst:

ΔGo = -(n)(F)(Δ Eo')

n= # of e- transferred

F= Faraday constant = 23 kcal/mol-volt

Δ Eo'= change in redox potential under standard conditions (all reactants at 1.0 M concentrations)

Pantothenate?

(PDH AND α -ketoglutarate inhibited=can't be biotin)

2 ATP, 2 NADH

electrical gradient and pH gradient (and chemical?)

measures substrate's affinity for e- as compared to standard rxn :

2H+ + 2e- → H2 Eo'= 0 volts

(-)Eo': e- donor stronger than H2=e- flow from NADH to H+

(+) Eo': e- donor weaker than H2 = will accept e- from H2

synthesis of 1 high E bond of ATP requires 12kcal/mol under physion conds

e- transfer from 1NADH = -52.3 kcal/mol → potential to make 4 high E bonds per e- pair

BUT only make 2.5 ATP = 60% efficiency

other 40% lost as heat

D→B→A→C

aconitase: dehyrdration, hydration

fumarase: hydration

succinate thiokinase

(no O2 → NADH built up → TCA cycle stopped)

1. Complex I

NADH:CoQ oxidoreductase/NADH dehydrogenase

-NADH converted back to NAD+ → transfers 2 e- to FMN (1 at a time) → e- transfered to Fe-S complexes (6-7) which have different redox potentials (goes from more - to more +) → 1 or 2 e- transferred to CoQ → QH2

-4 H+ pumped from matrix to intermembrane space per 2 e-

flavin mononucleotide

-derived from FAD

-flavin + ribitol + P

-flavin accepts e- one at a time → radical intermediate formed after 1 e- accepted

iron reduced/oxidized: Fe 3+ ↔ Fe2+

Coenzyme Q = ubiquinol

-derived from CoA

-can accept 1 or 2 e- → stable as either:

QH (radical) or

QH2 (completely reduced)

Pyruvate dehydrogenase

Succinate dehydrogenase

Ubiquinol-cytochrome C oxidoreductase

-QH2 donates 1 e- to CytbL → 2H+ pumped out + QH radical, donates other e- to Cyt C1→ 2H+ pumped out + CoQ formed

-Cyt C1 donates e- to Cyt C

-CytbL donates e- to CytbH which donates to CoQ and 1 H+ pumped in→ QH radical formed, receives e- from complex I and H+ pumped in → QH2

(total of four H+ pumped out)

blood flow greatly decreased → no O2 → everything reduced in chain = QH or QH2

-when O2 is restored QH radical can react w/ O2 → radical oxygen form

Cyt C

contain heme groups → Fe 3+ + e-↔ Fe 2+

cytochrome oxidase

Cyt C donates e- 1 at a time to Cyta1:CuA → donates e- to Cyta3:CuB

→ 2 H+ pumped out

once 4 e- collected w/n complex IV O2 reduced to H2O:

(1/2 O2 + 2H+ → H2O) x2 (b/c 1/2 O2 doesn't actually exist)

Cu+2 + e- ↔ Cu +1

contains succinate dehydrogenase

-entry point for FADH2 from TCA cycle (weaker reducing agent, enters chain later NADH)

-2 e- donated to FAD → Fe-S → CoQ (1 or 2 e- at a time)

*no proton extruxion (E transfers are too low)

10 H+

6 H+

proton gradient established across inner mito membrane:

-high [H+] outside than inside

-electrical and pH (concentration) gradient

- entry of H+ into mito is energetically favorable → 4 H+ required to make 1 high E bond

two components:

1. Δ pH: (pH matrix > pH intermembrane space)

2. Δ ψ: [H+] matrix < intermembrane space)

→ electrochemical gradient

F0: pore

-membrane ebedded

-C subunits

F1: Headpiece

- gamma (assymetric(

-α x3

-ß x3

H+ flows through pore down its electrochemical grad → c subunit changes → gamma rotates → α -ß pairs change conformation based on which part of gamma is interacting with it → bound ATP is released, ADP + Pi is converted to bound ATP, new exposed dimer binds ADP

(4 H+ = movement of α -ß to next conformation?)

Making ATP is reversible

release of ATP requires E

-blocks ATP synthesis by blocking F0 pore (proton channel) → H+ cant go through pore → respiration blocked due to coupling of ATP synthesis and e- flow

!. e- transfer chain must be assymetrically oriented across the membrane such that protons are ejected

2. Mito must be capable of ejecting protons in the presence of substrate and O2

(measurable decrease in pH outside)

3. permeabilizing membranes to protons should disrupt oxidation and phosphoryltion

(add detergent →holes in membrane→ no H+ gradient created = no pH change)

4. mito must contain a proton ddriven ATP synthase

ATP will be synthesized

(artifical H+ gradient created)

4 H+ into ATP synthase required to make 1 high E bond (ATP) = 3 H+ into ATP synthase + 1 H+ to bring Pi

NADH: 1 pair of e- = 10 H+ → 2.5 ATP (P:O 2.5)

FADH2: 1 pair of e- = 6 H+ → 1.5 ATP (P:O 1.5)

under normal conditions: disrupt one then disrupt the other

-gets cytosolic NADH e- into e- transport chain

cytosolic glycerol-3-phosphate dehydrogenase:

DHAP + NADH + H+ → NAD+ + Glycerol-3-phosphate

mitochondrial glycerol-3-phosphate dehydrogenase: (embedded in membrane on cyoplasmic side)

glycerol-3-phosphate + FAD → DHAP + FADH2

e- then transferred to CoQ → complex III

-loss of potential: 1.5 ATP produced

-skeletal mm. and brain mito use b/c faster

-no cmpds transported into mito

overall equation: NADHout + NADH+in → NAD+out + NADHin

-no E loss

-liver

-slow

key enzymes:

1. malate DH (cyto and matrix isozymes)

2. glutamate aminotransferase (matrix)

3. aspartate aminotransferase (cyto)

two transporters:

1. malate-α -ketoglutarate transporter

2. glutamate-aspartate transporter

(cytoplasm) OAA + NADH → NAD+ + malate → malate - α -ketoglutarate transporter → (matrix) malate + NAD+ → NADH + OAA

OAA + glutamate → α - ketoglutarate + aspartate

α - ketoglutarate → malate- α - ketoglutarate transporter → cytoplasm

aspartate → glutamate-aspartate transporter → cytoplasm

aspartate + α -ketoglutarate → glutamate + OAA

glutamate → glutamate-aspartate transporter

No NADH transporter in mito IM

1. malate aspartate shuttle (liver)

2. glycerol phosphate shuttle (mm., brain)

-cause membrane to become permeable to H+ → dissipate e- gradient → no ATP synthesis → respiration continues at increased rate in attempt to re-establish H+ gradient

UCP1: thermogenin

UCP2-5: unknown function

(drug companies trying to create drugs to partially uncouple → weight loss)

-natural uncoupler (babies, brown fat)

-activated by Norepi

-dissipation of proton gradient → heat production

1. block e- flow along the chain

2. block ATP synthase activity

3. allow free ion flow across inner mito membrane

enhanced H+ gradient

1. Sites w/n ETC

2. ATP Synthase

3. Uncouplers

4. ATP/ADP exchange

Complex I blocked: specific inhibition of e- transfer from Fe-S to CoQ

blocks complex III: CytC can't accept e- from it

inhibit complex IV: bind Fe in Cyts preventing e- transfer

inhibit complex IV: bind Fe in Cyts preventing e- transfer

a. Rotenone - I

b. Amytal - I

c. Antimycin A- III

d CN, CO - IV

a. oligiomycin- block H+ entry

b. DCCD- block H+ entry

a. CCCP - permeable to H+

b. DNP - permeable to H+

c. Valinomycin - permeable to K+ → destrs elec. grad

d. Thermogenin - permeable to H+

atractyloside- blocks ADP entry into mito → ATP synthase can't work

*ATP synthesis regulated by levels of available ADP, Pi

Two transporters embedded in IM:

*both driven by H+ gradient

1. Adenosine Nucleotide Translocase: antiporter

ADP(3-) → matrix (→ ATP synthase)

ATP (4-) → intermembrane space

2. Phosphate translocase: symporter

H2PO4- and H+ → matrix (H2PO4- → ATP synthase)

-by Energy Charge: (and O2)

normal= 0.8

<0.8 → E production stimulated

> 0.8 → ADP supplies in mito become rate limiting → ATP synthesis stops

Glycerol-phosphate shuttle: 30 ATP

malate-aspartate shuttle: 32

-affect organs w/ high E requirements = NS and mm.

-partial activity loss in complexes I, III, IV → exercise intolerance

-range of symptoms

1. deletions of mtDNA

2. Point mutations in tRNA or rRNA genes

3. missense mutations

1. Kearns-Sayre syndrome (nerve and mm.)

2. Pearson Syndrome (bone marrow)

a. MERRF (myoclonic epilepsy and ragged red fiber disease): tRNA lys

b. MELAS (mitco encephalopathy, lactic acidosis and strokelike episodes): 80% tRNA leu

1. Lehigh disease (nerve and mm., 25% in ATP stnthase)

2. LHON (leber hereditary optic neuropathy): 90% complex I

mutations in certain enzymes (cyto isoform) → tumer production:

1. succinate DH → succinate accummulation

-familial paraganglioma, NS

-loss of function

2. Fumarase → fumarate accumulation

-autosomal dom.:

--cutaneous and uterine leiomyomas

--hereditary leiomylomatosis and renal cancer syndrome (age of onset 25-30)

-autosomal recessive:

--fumarate deficiency: progressive encephalopathy, cerebral strophy, seizures, hypotonia, renal developmental delay

-loss of function

-enzyme is homotetramer

3. isocitrate DH: gain of function mutation so can make 2-hydroxyglutarate instead of α -ketoglutarate

-gliomas, acute myeloid leukemia

**accumulation of key metabolites → altered gene expression and O2 sensing → tumor formation

-generated by IDH3

--also used for hydroxylation reactions: prolyl hydroxylase, collagen formation, N-methyl lysine hydrozylase = methylated histones, methy cytosine demethylase (genes w/ methyl C inactived)

-O2 + α -KG → succinate + CO2 + hydroxylated product

three isozymes:

IDH1- cyto, NADP+

IDH2- mito, NADP+

IDH3- mito, TCA, linked to NAD+

mutation of of Arg at active site of IDH1/2:

α -KG + NADPH → 2-hydroxyglutarate + NADP+

-mutation increases affinity for α -KG and decreases affinity for isocitrate at active site

-methylation of histone tail on lys → activation/inactivation of gene

normally: α -KH binds hydroxylase → converts methyl to hydroxymethyl → lost as formaldehyde, N loses a methyl

-2-hydroxyglutarate bins to active site of hydroxylase instead of α -KG → can't convert methyl to hydroxymethyl → alteration of gene expression

IDH mutations, SDH muts, fumarase muts → buikd up of succinate (or fumarate→ succinate) → product inhibition

→ inability to demethylate histones → alteration of gene expression during differentiation

α -KG dependent enzyme hydroxylates methyl group on cyt in promoter regions → removal

IDH, SH, FH muts: inhibition of hydroxylation → genome hypermethylation → altered gene expression and differentiation

causes: acute myeloid leukemia (AML)- methylation pattern of RBC genome resembles stem cell

Normal cellular O2 levels: HIF proline hydroxylation by prolyl hydroxylase→ ubiquitin added → degraded by proteasome

accummulation of 2-hydroxyglutarate, succinate, or fumarate → blocked hydroxylation by prolyl hydroxylase→ HIF active → increased glyvolysis and other events → cancer cell

block 2-hydroxyglutarate formation:

1. IDH-1 inhibitor:

→ reversed histone meth, slowed growth, promoted differentiation, didnt affect methylytosine demeth

2. IDH-2 inhibitor:

→> reversed DNA and histone hypermeth amd induced differentiation

MELAS (mutated tRNA leu)