Protein Biochem - eisenmesser Flashcards
Ketogenic aa
Leu
Lys
Both ketogenic and glucogenic aa
Phe
Tyr
Iso
Trp
“Pee TIP”
Post translational mod of which two proteins strengthen and modify Collagen? Why do we care?
4-hydroxyproline (Hyp)
- Interstrand H bonding
5-hydroxylysine (Hyl)
- interstrand X-links between Lys & Hyl
- forms covalent interstand X- links
*collagen is the most abundant protein in body
Both Prolyl hydoxylase and Lysel hydroxylase require what?
Ascorbate (VIt C) in order to convert Pro to Hyp and Lys to Hyl
(without it
Sx of scurvy
Reduced strength of collagen fibrils
Reduced vascular endothelium
→ swollen gums, bruising, anemia
gamma-carboxyglutamate (Gla) fxn
- what does it do
- what is it dependent on?
transmembrane prot that converts Glu to Gla by chelating Ca2+
Vit K dependent
Used by Prothrombin to target membranes
Which one degrades endogenous protein, and which extracellular prot?
Ubiquination, lysosomal degradation
Ubiquination: endogenous
- targets enzymes (E1-E3) to proteins (lysine) using ATP and direct them into proteosome
Lysosome: extracellular
- taken in by endocytosis to mix with digestive enzymes
Enzymatic degradation proteins in:
- Stomach
- intestine
Stomach
- Pepsin (peppy chief)
Intestine
- Trypsin
- Chymotrypsin
- Carboxypeptidase-A + B
How are these enzymes activated from zymogens
Stomach
- Pepsin (peppy chief)
Intestine
- Trypsin
- Chymotrypsin
- Carboxypeptidase-A
- Carboxypeptidase-B
Stomach
- Pepsinogen → Pepsin (peppy chief) (via HCl)
Intestine
- Trypsin (via enteropeptidase)
- Chymotrypsin (via trypsin)
- Carboxypeptidase-A + B (via enteropeptidase)
*note that Trypsin can activate all of the E in intestine
Which one of these are aspartic proteases, serine proteases, and metallocarboxypeptidases
- Carboxypeptidase-A+B
- Trypsin
- Chymotrypsin
- Pepsin (peppy chief)
Aspartic: (hydrolyzes N term)
- pepsin
Serine: (hydrolyzes C term)
- Trypsin + chymotrypsin
Metallocarboxypeptidases
(hydrolyzes C term)
- Carboxypeptidase A+B
Aminotransferases catalyze what?
Major goal?
Where?
Rxn of an a-keto acid and an amino acid to another a-keto acid and amino acid
- Reversible Keq=1
- Major goal: make Asp, NH3 for Urea cycle
- Mostly in cytosol (liver, kidney, intestine, muscle)
Transamination feeds what?
The urea cycle
- Major goal: make Asp, NH3 for Urea cycle
What does PLP form with the aminotransferase?
Forms “Schiff base” (a covalent linkage) with the aminotransferase,
Progressive hyperammonemia can cause
cerebral edema, coma, and death
Alanine + a-ketoglutarate → ?
aspartate + a-ketoglutarate → ?
ALT: pyruvate + glutamate
AST: oxaloacetate + glutamate
When you see ORNT1, think:
Ornithine INto mitochondria matrix
Citrulline OUT into cytosol
Control point for protein catabolism
- Directionality of ALT + AST regulated by products + substrates
- Carbamoyl phosphate synthetase I
- required activator: N-acetylglutamate - Glutamate dehydrogenase
- regulates NH3 transport
- depends on [ ] of Glu, a-ketoglut, NH3
Ammonia is toxic, so how do you transfer it from peripheral tissues to kidneys and liver?
Glutamine is used to hold 2 Ns
Glutamate (1 N) + NH3 + ATP + (Gln synthetase) → glutamine (2 N)
What is produced for the transport of ammonia in:
Peripheral tissue:
Muscle:
Liver:
Peripheral tissue: Gln
Muscle: Ala
Liver: Urea
What role does the kidney play in the transport of ammonia?
Removes Urea
Removes Ammonia from Glutamate
What is significant about Glu dehydrogenase?
It is involved in the transport of ammonia
- converts Glutamate → a-ketoglutarate
- provides free NH3 for Urea cycle
- pee out NH3 (kidney) - Converts a-ketoglutarate + NH3 → Glutamate
- Glutamate can be converted to Ala for transport from muscle to liver
- Glutamaet can be converted to Glutamine for transport from periph tissue to liver
Activator vs inactivator of glutamate dehydrogenase
- ATP
- ADP
- GTP
- GDP
Inactivator
- ATP + GTP
Activator
- ADP + GDP
(mutation in ATP/GTP binding site → hyperinsulinism-hyperammonemia syndrome: cant shut off NH3 maker)
NO is derived from what?
Arginine via NO synthase
Arginine + NO synthase → Citrulline + NO
NO is a NT
Aspartate transamination yields _______. It can be converted to _____ in the krebs cycle TCA.
oxaloacetate, fumarate
aspartate and asparagine yields oxaloacetate
Asparagine yields ______ after hydrolysis catalyzed by the enzyme _____.
Asparagine → aspartate via asparaginase
aspartate can be converted to oxaloacetate just like asparagine
MSUD - what Enz is affected? Deficiency or lack of? This leads to build up of?
Deficiency of BCKDH
(branched chain a-keto acid dehydrogenase)
Build up of branched chain aa Val, Ile, Leu
Rank most active to less active
Tyrosine
T4
T3
T3 > Tyrosine > T4
T4 is made from tyrosine. T4 is a prohormone, so not very active
Order that they are made
Tyrosine
T4
T3
Tyrosine → T4 → T3
How is T3 and T4 made?
Thyroglobulin (TG) binds to I2 and gets iodinated. Then it undergoes protealysis to T3, T4
Thyroxin binding protein (TBP) carries it to blood
TSH
Stimulates Iodide (I-) uptake Stimulates release of T4, T3
Thyroid peroxidase
Oxidizes Iodide (I-) to (I2)
Thyroglobulin (TG)
Contains Tyr residues iodinated to form T4, T3
Thyroxin binding globulin (TBG)
Transports T4, T3
How does lead lead to anemia?
Can replace Zn in ALA dehydratase
- prevent production of porphobilinogen
Can replace Fe2+ in ferrochelatase
- prevents heme production
What enzyme is typically low in premature infants leading to jaundice babies? What other defects also involve this enzyme?
Bilirubin glucuronyl transferase
- use flourescent light to convert bilirubin to more polar products, allowing removal
- remember that this Enz allows unconj bilirubin to be converted to bilirubin, which will eventually become conj bili
- Crigler-Naijar syndrome
- Gilbert syndrome
Which is essential, which is non essential? Methionine, cysteine.
Methionine is essential
- cysteine can be made from Met (non essential)
*noet: cysteine can form disulfide crosslinks with other cysteines to form CYSTINE.
1st step of Met degradation
Methionine → SAM via
SAM synthase + ATP
SAM has an activated sulfur
SAM is also known as adoMet
How does methionine degrade and form cysteine?
Met + Ser = Cys
Met → SAM → SAH → Homocysteine (+Ser) → Cystathionine → Cysteine
(these rxns involve addn of ATP, demethylation, and removal of adenosine)
How do you regenerate Methionine
Need TWO coenzymes:
- THF
- Vit B12
- methyl group is transferred from THF to B12 to homocysteine
Which Vit are probably deficient if you have a build up of homocysteine?
B6 and B12
How is cysteine synth achieved from Homocysteine and serine?
Via cystathionine B-synthase (CBS) + PLP
PLP is a derivative of Vit B6
- it is also needed to convert cystathionine to cysteine.
Hyperhomocysteinemia levels
- tx
(Possible MTHFR enz defective and cant convert Homocysteine to methionine)
Low levels folate
Low levels B6, B12
- cysteine is now an essential vit
tx: folate, B6, B12
Homocystinuria defect
- tx
defect in cystathionine B Synthase (CBS)
- retardation, osteoporosis, vascular disease
- cysteine is now essential (just like hyperhomo)
Tx: Vit B6, to force CBS activity
Cysteinuria defect
- tx
defective transporter of cysteine (COAL)
- crystalization in kidneys (stones)
Tx: acetazolamide - makes cysteine more soluble
Is homocysteine good?
No! IS bad!
- Vascular disease
- Impaired wound healing
- Correlated to cancer (cervical)
SAM actions
- Methylation via SAM dependent enzymes
- Epigenetics (host defense)
- Cancer (meth/demeth)
- High levels of Met and SAM critical in maternal diet
- treat depression
THF is produced from Vit B9 (Folic acid) by what enzyme?
What drug blocks this enzyme?
Dihydrofolate reductase (DHER) - blocked by methotrexate
Methotrexate basically prevents production of THF
Why is Glutathione (GSH) important?
- Thiol (glutaTHIO) acts as a redox buffer to keep proteins in reduced form and regulate activity
- cofactor for other enzymes
- Protection against ROS (reduct H2O2)
Glutathione (GSH) is it active in unfolded (reduced) state or folded state?
Active in folded state
- disulfide bonds are cross linked and ready fo action
Example of how GSH acts as a redox buffer to keep proteins in reduced form and regulate activity
Keeps Fe2+ in ferrous state, capable of binding O2.
Fe3+ cannot bind O2
Why is Trp such an important aa?
- Trp can be metabolized to Pyruvate or acetyl-CoA
- Trp (with BH4 cofactor) make:
1. Serotonin
2. Melatonin
3. Niacin (critical cofactor for NAD)
Why are MAO inhibitors so helpful?
They block deamination like cray. Prevent the breakdown of DA.
