Pyruvate Metabolism 2
Terms
undefined, object
copy deck
- Oxidation # of carbons in one glucose:
- 0
- Oxidation # of carbons for 2 Pyruvate:
- +4 (+2/2pyruvate)
- Number of NAD+ reduced in pyruvate oxidation?
- 2 (1 molecule / pyruvate)
- Oxidation # of carbons for 6 CO2:
- +24 (+4/6CO2)
- Number of NAD+/FAD reduced in CO2 oxidation?
-
10 NAD + 2 FAD = 12
(2 electrons per NAD or FAD) - Sequence of oxidation from CH4 to CO2:
-
CH4 -> CH3-OH / CH3NH2/ H2C=CH2
-> CH2=O -> HCOOH -> CO2 - # electrons released in each oxidation:
- 2
- Always present at an oxidation:
- NAD+ or FADH+
-
Enzyme that converts pyruvate to alanine:
-Coenzyme
-Cellular site
-Rev/irrev -
Alanine aminotransferase (ALT)
Coenzyme = PLP
Site = Cytosol
Reversible -
Enzyme that converts pyruvate to lactate:
-Cellular site
-Rev/irrev -
Lactate Dehydrogenase (LD)
Cell site: Cytosol
Reversible -
Enzyme that converts Pyruvate to Oxaloacetate:
-Coenzyme
-Cellular site
-Rev/irrev -
Pyruvate Carboxylase
-Biotin
-Mito matrix in liver/kidney
-Irreversible -
Enzyme that converts Pyruvate to AcCoA:
-Coenzyme
-Cellular site
-Rev/irrev -
Pyruvate dehydrogenase complex
-TPP, Lipoic acid, FAD
-Mito matrix
-Irreversible -
Enzyme that converts Pyruvate to Acetaldehyde -> Alcohol:
-Coenzyme
-Cellular site
-Rev/irrev -
Pyruvate decarboxylase
-TPP
-Microbes only NOT MAMMALS
-Irreversible - Why is Pyruvate so important?
- It sits at a critical branchpoint with 4 possible fates:
- What are the 4 fates of pyruvate? (things it can be converted to)
-
1. Alanine
2. Lactate
3. AcCoA
4. Oxaloacetate - Where is the energy in pyruvate?
-
-Its ability to be further oxidized
-The 2 NADH produced in glycolysis (G3P dehydrogenase) - What important factor determines the fate of pyruvate?
- Whether oxygen is available or not.
- What is the oxidation number of each molecule in going from methane to CO2 via methanol, formaldehyde, formic acid, CO2?
-
1. Methane = -4
2. Methanol = -2
3. Formaldehyde = 0
4. Formic acid = +2
5. Carbon Dioxide = +4 - Back to the fates of pyruvate:
- ok
- Why/when does pyruvate get converted to Lactate and Alanine?
- When skeletal muscles don't get enough O2 like during intense exercise.
- What 2 things need to happen during intense exercise?
-
1. Replenish NAD+
2. Resynthesize glucose (liver) - What is the body's simplest solution for achieving these goals?
-
1. Break down pyruvate to lactate
2. Send lactate to liver to make glucose - Why occurs in the similar process that converts pyruvate to L-alanine instead of lactate?
-
1. L-glutamate donates NH3 to pyruvate - makes L-alanine
2. NADH -> NAD+ at the same time; replenishes it for tissue. - How is L-Alanine useful?
- Sent to the liver, it supports gluconeogenesis.
- What is required for pyruvate to participate in gluconeogenesis in the liver?
- Conversion to PEP via 2-step process
- What is the first step in going from Pyruvate -> PEP?
- Conversion to Oxaloacetate
- What happens to pyruvate when oxygen is PLENTIFUL?
- Gets oxidized to AcCoA
- Why is AcCoA a very important irreversible step in biology?
- BECAUSE IT CANNOT BE CONVERTED BACK TO GLUCOSE.
- How does the body prevent overproduction of AcCoA from glucose (depleting glucose)?
- By tightly regulating the enzyme for the reaction - PDH complex.
- What reaction with Pyruvate occurs in microbes but not mammals?
- Pyruvate->Acetaldehyde/Ethanol
- Where in the body does gluconeogenesis predominantly occur?
-
90% in liver
10% in kidney - What are the general characteristics of Pyruvate? (3 things)
-
1. Strong acid (pKa 2.5)
2. Simplest a-keto acid
3. Low concentration - always gets converted to something. - What really is the purpose of ALT?
- To convert pyruvate to a product that is suitable for transport to the liver.
- And the good byproduct of this conversion is:
- Regeneration of NAD+ for the cell
- What additional enzyme is necessary for the proper action of ALT?
- Glutamate dehydrogenase (GDH)
- 3 good things accomplished by the ALT reaction:
-
1. NADH is oxidized to NAD+ and glycolysis can continue
2. L-alanine (pyruvate equiv) can make glucose in liver.
3. NH3 is converted to derivative for safe transport to liver; prevents toxicity. - How does LDH accomplish conversion of pyruvate to lactate?
- By using NADH to donate a proton to C2 of pyruvate
- What about LDH makes it a good enzyme for this conversion?
-
Its reactive site contains
-Arg to hold on to COO-
-His to donate proton to carbonyl oxygen -> -OH - How does NADH donate its H- to pyruvate?
- The H- ion attacks C2 and bumps electrons up to grab on to histidine's proton.
- What is important about NADH's participation in the LDH rxn?
- Sterespecific - H donation comes from only one side of the NADH ring.
-
where is PDH complex located?
(pyruvate dehydrogenase) - In the mitochondrial matrix
-
What is PDH composed of?
(3 components) -
ACTUALLY THREE ENZYMES:
E1. Pyruvate dehydrogenase
E2. Dihydrolipoyl transacetylase
E3. Dihydrolipoyl dehydrogenase - What 3 cofactors does PDH use?
-
1. TPP (thiamine pyrophosphate)
2. Riboflavin
3. FAD -
What happens to Pyruvate in step 1 of PDH?
-Enzyme component
-Cofactor -
Enzyme = PDH
Cofactor = TPP
Pyruvate -> Hydroxyethyl TPP + CO2 (lost) -
What happens to Hydroxyethyl TPP in step 2 of PDH?
-Enzyme component -
Enzyme2 = Dihydrolipoyl transacetylase
-Hydroxyethyl TPP has neg charged carbon; attacks S of lipoamide
-Produces Acetyl-dihydrolipoamide - What happens in step three of PDH? What enzyme?
- Still at Enzyme 2; CoA is incorporated into intermediate to produce Acetyl CoA.
- How is the reduced lipoamide generated by Acetyl CoA production OXIDIZED to regenerate it?
- By E3, dihydrolipoyl dehydrogenase
- What cofactor and substrate is used by E3?
-
-FAD cofactor
-NAD+ substrate - Since NADH is produced in AcCoA production, this is obviously not something you want to be doing in strenuously exercising muscle.
- Agreeed.
- What is special about lipoamide?
- It has a long swinging arm that acts as a Lysine Tether to transport Acetyl group to active site for CoA addition
- What type of reaction is catalyzed by PDH complex?
- Oxidative decarboxylation
- Is dihydrolipoamide good or bad?
- Good if it can be regenerated, but you don't want to stay there. E3 better regenerate lipoamide if you want to keep producing AcCoA
- What key role does PDH play in glucose metabolism?
- Couples Glycolysis and TCA
- 3 goals accomplished by PDH:
-
1. Pyruvate -> AcCoA
2. Energy of oxidative decarboxylation is CAPTURED
3. Complex is regulated - In what 2 forms is the energy of the PDH complex captured?
-
1. NADH -> for further use
2. Hi energy thioester bond of AcCoA - Which components of PDH are reversible/irreversible reactions?
-
E1 = irreversible
(overall rxn is irreversible)
E2 and E3 = reversible - In what 2 ways is PDH regulated?
-
1. Feedback inhibition by NADH and AcCoA
2. Interconversion between active/nonactive forms -
What form of PDH is
-Active
-Nonactive
What makes these forms? -
Active = DEphosphorylated
Nonactive = phosphorylated
PDH phosphatase/PDH kinase -
Which enzyme turns on PDH?
Which enzyme turns it off? -
PDH Phosphatase turns PDH on
PDH Kinase turns PDH off - What will make PDH Kinase act on PDH?
-
High Energy State metabolites:
-AcCoA
-NADH
-ATP
Don't need Kreb's cycle - What will make PDH Phosphatase turn PDH on?
-
Low Energy State molecules:
-Mg2+
-Ca2+
-Insulin in adipose - Why does Insulin turn on PDH via PDH phosphatase?
- B/c it signals high blood glucose; adipocytes need AcCoA to make fat.
- What is the message Insulin gives adipose tissue in fed state?
-
-Turns on PDH phosphatase
-Turns on PDH
-Pyruvate -> AcCoA
-AcCoA -> FA biosynthesis - TPP is derived from:
- Thiamine - vitamin B1
- Deficiency of Thiamine leads to:
- Beriberi
- What is beriberi? who gets it?
-
Disorder w/ neurologic/CV symp.
-Far East people who eat rice
-ALCOHOLICS - What term describes the condition of drinking ethanol rather than thiamine-containing foods?
- Alcoholic Polyneuropathy
- What does Thiamine deficiency in alcoholics irreversibly lead to?
- Wernicke-Korsakoff Syndrome
- What do all enzymes that require TPP (thiamine pyrophosphate) do?
- Transfer activated aldehyde units
- What are the 4 known Thiamine requiring mammalian enzymes?
-
-Transketolase (PPP)
-PDH (pyruvate mtbsm)
-a-Ketoglutarate Dehydrog (TCA)
-Branched chain of above (AA) - What is the substrate for all of these enzymes? In the last 3?
-
All use a ketone substrate
Last three involve a-ketoacid substrates. - How is Beriberi diagnosed?
- RBC Transketolase assay
- What is deficiency of E3?
- Leigh's disease - less than 10 cases known
-
Rxn catalyzed by Pyruvate carboxylase?
-Coenzyme
-Substrate -
Pyruvate -> Oxaloacetate
Coenzyme = Biotin
Substrate = ATP - What is the key feature of all Biotin-dependent enzymes?
- Reaction occurs in 2 steps - first step attaches CO2 to biotin via ATP -> ADP + Pi
- 2 steps in Pyruvate carboxylase reaction:
-
1. HCO3 attached to Biotin via ATP cleavage
2. CarboxyBiotin + Pyruvate -> Oxaloacetat + Biotin - ONlY 2 OTHER BIOTIN-DEPENDENT ENZYMES IN MAMMALIAN BIOCHEM:
-
-Propionyl-CoA Carboxylase
-AcetylCoA Carboxylase
(both involved in FA metblsm) - What is the coenzyme used by Pyruvate Decarboxylase? What is this reaction specific to?
- TPP - only in MICROBES
- What is the Pyruvate decarboxylase reaction?
- Just like PDH but no NAD used; NOT A REDOX
- What does microbe Pyruvate decarboxylase produce?
- Ethanol - in microbes in the human gut too.
- When the bloodstream is cleared of glucose, but you're not fasting, what does the liver do?
- Sends glucose to muscles (by breaking down glycogen)
- What do the muscles do with glucose?
- Glycolysis - which generates pyruvate first before TCA.
- What do muscles do with Pyruvate?
-
If O2 available, TCA cycle.
If O2 unavailable, convert to lactate and alanine - less ATP gets made, but NAD+ regenerated. - What happens to Lactate and Alanine?
- They're sent to the liver
- What does the liver do with Lactate and Alanine?
- Use it to remake pyruvate for gluconeogenesis
- Which steps of gluconeogenesis require ATP?
-
-Pyruvate -> oxaloacetate
-Oxaloacetate -> PEP
-PEP -> Glucose - How does the liver generate ATP?
- By breaking down fat -> AcCoA and using that for the TCA cycle
- What is this shuttling of pyruvate breakdown products from skeletal muscle to liver called?
- The cori cycle
- How can the liver still run the TCA cycle when muscles are unable to b/c of anaerobic conditions?
- The liver has more O2 in general.