Oxidative Phosphorylation Flashcards
(27 cards)
Describe regulation of the PDC.
PDC has pyruvate dehydrogenase phosphatase and pyruvate dehydrogenase kinase tightly bound to it. They act by either phoshporylating or dephosphorylating E1 of the PDC.
PDC is active when dephosphorylated.
PDC is activated by substrates and low energy sinals such as elevated NAD and ADP. High Insulin favors activation by acitvating PDP. Also activated by calcium and Mg which allosterically activate PDP, CoA, pyruvate and NAD and ADP inhibit PDK,
PDC is inactivated by end products and high energy signals such as NADH and ATP which allosterically activate PDK. Inhibition is favored under fasting where acetyl CoA and NADH are high due to fatty acid oxidation. also Arsenite inhibits via PDC inhibition by binding to Lipoic acid in E2.
What does Arsenite do?
It inhibits PDC by binding to Lipoic acid in E2. Arsenite links lipoic acids to SH groups and acts as a suicide inhibitor that binds to thiol groups irreversibly and limits availibility of Lipoic acid. This effects PDC but also enzymes that use lipoic acid such as a-KG DH and BCA DH. This is a slow poison becasue it takes time for the effects of impacting the enzymes to build up.
What are the three prostethic groups on the PDC?
TPP, Lipoic acid and FAD.
CoA and NAD are co substrates that temporarily associate. CoA and NAD are activators by inhibiting PDK.
What is the clinical significance of PDC with a phosphatase deficiency?
It links the TCA to glycolysis. With a phosphatase deficiency the PDC is always INACTIVATED. This results in Glucose going to lactate rather than Acetyl CoA and results in constant lactic acidosis. This impacts the CNS the most and alanine intake is restricted. Ketogenic diet is recommended.
How many high energy substrates are produced from the TCA?
10 as there are two cycles with one pyruvate used.
2 FADH from Succinate to Fumarate via Succinate DH (aka Complex 2)
2 NADH from Isocitrate to a-KG via IsocitrateDH (RLS)
2NADH from a-KG to Succinyl-CoA via a-KG DH.
2GTP from Succinyl-CoA to Succinate via substrate level phosphorylation Succinate thiokinase
(NADH accepts 2 electrons as a Hydride ion to make NADH and H+)
If two moles of pyruvate were used we would have 25 ATP equivalent high energy molecules
RLS and regulated steps of TCA?
Isocitrate dehydrogenase is RLS
Citrate Synthase is regulated(step1), Isocitrate DH is regulated (step 3), a-KG DH (step4) is regulated
What happens when cellular levels of ATP are increased and decreased?
The activity of TCA triggers inhibition of TCA as the ETC is inhibited when ATP is increased.
When ATP is decreased TCA cycle increases as that indicates energy is low.
What are the two major anaplerotic reactions of TCA cycle?
Degradation of amino acids and carboxylation of pyruvate
What amino acids contribute to Fumarate?
Phe, Tyr, Asp
What amino acids contribute to OAA?
Asn Asp
What amino acids contribute to a-KG?
Gln, Pro, His, Arg they all convert to Glutamate which goes to a-kg
What amino acids contribute to succinyl CoA?
Thr, Met,Ile, Val which all go to Propionyl CoA to make succinyl coa
How do the TCA intermediates contribute to Glucose and lipid synthesis?
Malate can leave the mt matrix and be converted into OAA and PEP and make glucose.
Citrate leaves the mt matrix and goes into FAS.
2-Oxoglutaric aciduria?
A rare disorder with global dev delay and severe neurological problems in infants. Results in metabolic acidosis, severe microcephaly and mental retardation.
Fumarase deficiency?
Characterized by severe neurological impairment. Fatal outcome withtin 2 years of life. Results in encephalomyopathy, dystonia, increased urinary excretion of fumarate, succinate, a-kg, citrate, autosomal recessive
How does calcium play an important role in regulation of PDC?
In exercising muscle ca stimulates PDC by bindnig directly to PDP. In cardiac mm Ca inhibits PDK leading to activation of PDC.
SCS deficiency?
Associated with mutations of SUCLA 2 and SUCLG1 they encode beta subunit of ADP forming ACS and alpha subunit of SCS. Oncometabolites of TCA such as citrate and 2-hydroxyl glutarate accumulate and decrease TCA cycle. Mt depletion syndrome asssociated with hypotonia, dystonia, mm atrophy and neuro hearing impairment.
what constitutes PMF?
pH gradient and membrane potential
A woman is brought into the ER from an aparent overdose. The man who brought her says it was on barbituates. In regards to oxidative phosphorylation and ETC, what is happening?
The barbiturates bind to Complex one at the CoQ binding site and prevent electron transfer from internal Fe-S centers to coenzyme Q. CoQ can still be reduced by succinate dehydrogenase and CoQ oxidoreductase.
If you are doing an enzyme assay to test cellular fractions for contamination with extraneous material, what enzymes could be used to test for contamination with inner membrane and matrix in the mitochondria?
a. Pyr. DH in matrix and Cytochrome C oxidase IM
b. PK matrix and FAD dependent G3PDH IM
c. Thermogenin matrix and succinate DH IM
d. NADH DH matrix and a-KG DH IM
NADH Dehydrogenase and a-kg dehydrogenase can be used. NADH DH is complex one in oxidative phosphorylation and is located in inner mitochondrial membrane. This would be ideal to check to see if the matrix has been contaminated with the inner membrane. A-KG DH is soluble enzyme of TCA and this occurs in the matrix.
PK is in cytosol as it is glycolysis enzyme,FAD dependendent G3P DH is located on outside of inner mito membrane facing IMS.
A 10 wk old boy was admitted to metabolic unit of peds hospital with irregularities in brain development. after birth he was in respiratory distress, showed hypotonia, fed poorly, and had frequent siezures. His lab results showed pH 7.2, elevated serum pyruvate, lactate and alanine. Decreased Citrate. What kind of deficiency does he have what should he be treated with?
a. Low galactose diet ; GALT
b. coQ and carnitine ; Orotic aciduria
c. uncooked corn starch meals ; malabsorption
d. allopurinol ; poisoned
e. dichloroacetate thiamine and citrate ; PDC
E because low citrate and high pyruvate indicate pyruvate dehydrogenase activity. This explains hte increased lactate and alanine. Dichloroacetate inhibts Pyr DH kinase and thiamine is a cofactor of pyruvate dehydronase and citrate treats acidemia.
A patient is admitted to the ER with a fever of 105.8F he is flushed with sweaty skin, tachycardia, rapid respiration. He complains of nausea malaise and palpatations. He admits he took natural weight loss supplements, what is the active ingredient in this supplement?
a. Cyanide
b. 2,4-Dinitrophenol
c. Antimycin A
d. Ologomycin
2,4 Dinitrophenol it is an uncoupler and causes protons to leak back into the matrix disrupting the proton gradient causing ATP to be released as heat.
Arsenite is a poison that causes toxicity by forming chemical bonds with SH groups especially when the groups are close together. Which mitochondrial enzyme uses a cofactor susceptible to this poisoning?
The E2 subunit of pyruvate dehydrogenase complex uses lipoamide to transfer the decarboxylated products to Coenzyme A. Lipoamide gets converted to an intermediate in the process and this intermediate has two close spaced SH groups.
If ATP to ADP ratio is high what happens with oxidative phosphorylation?
There is a lot of excess energy so ATP synthase is inhibited, which increases H gradient and therefore decreases the electron transport and hydrogen pumping, slowing down TCA cycle and decreasing glycolysis.
