Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biochemistry III > WK09L2 - Biotransformation II (Ben) > Flashcards

WK09L2 - Biotransformation II (Ben) Flashcards

1
Q

What is the overall reaction performed by a CYP450 mono-oxygenase enzyme?

A

endo-/xenobiotic + O2 + NADPH + H+

becomes

oxygenated endo-/xenobiotic + H2O + NADP+

(one O of O2 goes to the biotic… one goes to water… both H atoms go to water)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the 6 types of phase II conjugation reactions in biotransformation?

(in order of frequency/importance in the body)

A
  1. Glucuronidation
  2. Sulfation
  3. Glutathione conjugation
  4. Amino acid conjugation
  5. Methylation
  6. Acetylation / Acylation

GSGAMA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the co-factor used in glucuronidation reactions?

What is it a derivative of and how is it made?

Other than biotransformation, what is it used for?

A

UDP-glucuronate

  • derivative of UDP-glucose
  • UDP-glucose is dehydrogenated leaving it with -COO- on C6 of its ring (using 2 NAD+)
  • also used in formation of mucopolysaccharides
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the enzyme responsible for glucuronidation?

A

UDP-glucuronyl transferase (UGT)

  • a superfamily of enzymes broken into subfamilies 1 and 2

(subfamily 2 has further divisions into A and B categories)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are 3 examples of glucuronidated xenobiotics?

(w/ 3 examples of functional groups that can be glucuronidated)

A
  1. Acetaminophen (on the phenolic -OH)
  2. Ibuprofen (on a -COOH group)
  3. p-Aminosalicylic Acid (on the amino group)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the major substrates of the UGT1 and UGT2 isoenzymes?

A
  • UGT1: fenols, bilirubin
  • UGT2: steroids, bile acid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are some (6) inducers of UGT enzymes?

A
  1. Morphine
  2. Steroids
  3. Bile Acids
  4. Retionids
  5. Polycyclic Aryl Hydrocarbons
  6. Heterocyclic Aryl Hydrocarbons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where are UDP enzymes located?

What does this mean for their substrates and products?

How is this unique?

A

Embedded in the ER membrane with active sites in ER lumen

  • UDP-glucuronate must enter and glucuronide conjugates must leave the ER via transporters
  • is the only conjugation occuring in the ER lumen

(others are in the cytosol)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the 2nd most important kind of conjugation?

Via what enzyme + where is it found?

A

Sulfation

  • addition of inorganic sulfate (to an -OH group or amine)
  • via sulfotransferase enzymes in the cytosol
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the co-factor which donates the inorganic sulfate in sulfation?

How is it made?

A

PAPS

(3’-Phosphoadenosine-5’-phosphosulfate)

  • made in 2 steps by PAPS synthetase using sulfate from Cys metabolism and 2 ATP

(enzyme is like a kinase, but transfers sulfate instead of phosphate)

  • creates an anhydride bond btwn sulfate + phosphate with high group transfer potential
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the general types of substrates for sulfation?

And a few specific examples?

A
  • General: phenols, alcohols, aromatic amines
  • Examples:
    • estrone
    • 3-OH-coumarin
    • acetaminophen (not only glucuronidated!)
    • methyl-DOPA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the 3rd most important kind of conjugation?

Via what enzyme + where is it found?

A

Glutathione conjugation

  • via glutathione S-transferase enzymes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the structure of glutathione.

And its general functions?

A

Is a tripeptide made of Glu, Cys, and Gly with an unusual peptide bond btwn Glu-Cys at the γ-carboxyl (rather than α)

  • important endogenous water-soluble anti-oxidant
  • forms disulfide when oxidized by ROSs
  • involved in conjugation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the molecular/energetic basis of glutathione conjugation?

(As in, what part of glutathione reacts with what part of the molecule to be conjugated?)

A

Reactivity of glutathione’s -SH group with an electrophilic reagent (R-X in img)

Results in thioether formation btwn the electrophile and glutathion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens in glutathione conjugation after glutathione is added to the endo-/xenobiotic in question?

A
  • Glu is hydrolyzed by a glutamyl transferase leaving only Cys and Gly
  • Then Gly is hydrolyzed by cysteinyl-glycinase leaving only Cys
  • And acetyl transferase now acetylates Cys amino grp leaving a mercapturic acid derivative
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the most importan endogenous substrates for glutathione conjugation?

A

Leukotrienes

  • several different leukotrienes are just the products of each step in the removal of the amino acid constituents of glutathione (when it is conjugated to arachidonic acid) mentioned in the previous card
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the 4th most important kind of conjugation?

Via what enzymes + where are they found?

A

Amino acid conjugation

  • via acyltransferases
  • found in mitochondria (at least the glycine transferase is)
18
Q

What two AAs are most commonly used in amino acid conjugation?

A

Glycine

and

Taurine (made from Cys)

19
Q

What is the unique first step in amino acid conjugation?

And an example of this with a molecule that is AA conjugated?

A

Activation of the molecule to be conjugated…

  • ex: carboxyl group of benzoic acid is bound to S-CoA using energy from one ATP via an acyl-CoA synthetase enzyme
20
Q

After activation of the substrate molecule, what is the last step in amino acid conjugation?

A

The activated molecule is transferred to an amino acid using an N-acyltransferase enzyme

(Acyl-CoA glycinetransferase in the case of glycine conjugation)

21
Q

In general, what are the substrates for amino acid conjugation?

And several specific examples?

A
  • General: Acyl-CoA derivatives of carboxylic acids
  • Examples:
    • Benzoic Acid
    • Salicylic Acid
    • Nicotinic Acid
    • Cinnamic Acid
    • Bile Acids (cholic acid, deoxycholic acid)
22
Q

What is the 5th most important kind of conjugation reaction?

What functional group can this conjugation be done to?

Via what enzymes + where are they found?

A

Acetylation of amine groups

  • via acetyltransferase enzymes either free in cytosol or ER-bound (with active sites in cytosol)
23
Q

What are the general substrates for acetylation?

And some specific examples?

A
  • General: amides
  • Examples:
    • sulfonamides
    • clonazepam
    • mescaline
    • dapsone
    • isonazid
24
Q

What is the 6th most important kind of conjugation reaction?

What functional groups are conjugated in this way?

Via what enzymes + where are they located?

A

Methylation

  • usually phenolic -OH grps, sometimes amino groups

- via methyltransferase enzymes in cytosol

25
Q

What is the common donor of methyl groups for methylation conjugations?

How is it made?

A

S-adenosyl methionine

  • made by methionine adenosyltransferase using ATP and yielding PPi and Pi
26
Q

What are the general substrates for methylation?

And some specific examples?

A
  • General: catecholamines, phenols and amines
  • Examples:
    • Dopamine
    • Epinephrine
    • Pyridine
    • Histamine
    • Thiouracil
27
Q

Give an example of how the location of a methylation on a molecule can have drastic differences on the activity of the product.

A

With norepinephrine…

  • Methylation of the phenolic -OH (by COMT) leads to an inactive product
  • Methylation of the amine (by PMNT) leads to epinephrine formation
28
Q

Conjugation products can be deconjugated resulting in re-creation of an active intermediate…

Give an example of this in the body.

A
  • Estrone is created from androstenedione by aromatase in the uterus (and other tissues)
  • It is then sulfated by sulfotransferases in the liver to estrone-sulphate
  • Some breast tumors contain high amounts of steroid sulfatase enzymes which desulfate estrone-sulphate, re-activating it.
  • (Estrone then acts as a growth factor for these tumors.)
29
Q

What are the 2 routes for elimination of conjugated molecules from the liver?

A
  • Blood –> filtration in the kidney –> excretion via urine
  • Bile –> secretion into the GI tract –> excretion via feces
30
Q

Describe the entry and exit of endo-/xenobiotics into and out of hepatocytes in the process of biotransformation.

A
  • Entry - usually passive transport into the hepatocyte via membrane transporters (uptake transporters = acronyms on left of img)
  • Exit - almost always active transport, transporters have specificity for certain structural features to determine excretion to bile or blood (acronyms on right)
31
Q

What are some of the transporters responsible for secretion of conjugated molecules from hepatocytes to blood?

To bile?

A
  • Blood - MRP1/3/6 (multi-drug resistance protein)
  • Bile
    • ​MRP2
    • MDR1/3 (also multi-drug resistance protein)
    • BSEP (Bile Salt Export Pump)
32
Q

What class of endo-/xenobiotic transport molecules used for removal of molecules from cells uses ATP?

Describe them + their function.

A

ABC transporters

(ABC = ATP-binding cassette)

  • 12 TM helices
  • 2 nucleotide binding domains
  • Some export conjugated molecules from the cytosol, others export unconjugated toxins from within the membrane itself as a protective mechanism.
33
Q

Describe how bile acid synthesis is a classic example of biotransformation.

A
  • Cholesterol is an endobiotic which can not be easily broken down.
  • Instead it is hydroxylated by several CYP450 enzymes in the liver (first = 7-α hydroxylase) to form cholate
  • Then cholate is conjugated to form glycocholate
34
Q

Describe the 1st phase biotransformation of heme.

A
  • It is first oxygenated by a CYP450 enzyme (heme oxygenase) to form biliverdin
  • Then it is reduced by biliverdin reductase to form bilirubin

(both steps using NADPH… two in step 1… one in step 2)

35
Q

Describe the 2nd phase biotransformation of heme.

(include the specific conjugating enzyme)

A
  • Bilirubin is then glucuronidated by UDP-glucuronyl transferase to form bilirubin diglucuronide

(the transferase is specifically UGT1A1)

36
Q

What transporter can bring bilirubin or bilirubin monoglucuronide into a hepatocyte?

And which transports bilirubin diglucuronide out of the cell?

A

entry - OATP1B1

exit - MRP2

(was pretty prominantly marked on a slide but not mentioned in lecture)

37
Q

What are the 2 diseases which are defects of conjugation in heme metabolism?

Their causes + effects?

A
  1. Gilbert syndrome - caused by mutation of promoter allele
    • slight elevation of unconj. bilirubin
    • mild jaundice
    • incr. paracetamol toxicity risk
  2. Crigler-Najjar syndrome - UGT1A1 mutation
    • elevated (mostly) unconjugated bilirubin
    • intense jaundice
    • kernicterus (bilirubin-related encephalopathy)
    • incr. paracetamol toxicity risk
38
Q

Which to diseases are defects of conjugate export in heme metabolism?

Their causes + effects?

A
  1. Dubin-johnson syndrome - MRP2 defect
    • elevated conjugated bilirubin (w/out liver enzyme elevation)
    • dark pigment in liver
    • normal lifespan
  2. Rotor Syndrome - defect unknown
    • elevated conjugated bilirubin
    • no liver pigmentation
39
Q

What receptor is responsible for CYP3A induction?

What binds it?

What happens when it is bound?

A

Pregnane X Receptor

  • endogenous ligands = steroid hormones
  • forms heterodimer with retinoid X receptor leading to upregulation of CYP3A
40
Q

Describe the general structure of some of the nuclear receptors involved in CYP transcription regulation.

Other than PXR mentioned in the last card, name 2 and their regulated CYP enzymes.

A
  • are ligand-dependent
  • contain a double zinc finger DNA binding domain (DBD)
  • also have a larger ligand binding domain (LBD)

CAR regulates CYP2B (constitutive androstane receptor)
VDR regulates CYP27 (vitamin D receptor)

41
Q

What molecule is important in the control of phase II enzymes?

(didn’t go over this slide in lecture… no clue abt it… just throwing it in)

A

Nrf2

Biochemistry III (35 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions