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Biochemistry I > Chapter 6: Reversible Inhibitors > Flashcards

Chapter 6: Reversible Inhibitors Flashcards

1
Q

Reversible inhibitors

A
  • Reduce the rate of enzyme-catalyzed reactions without permanently changing the structure of the enzyme
  • Utilize weak, non-covalent interactions
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2
Q

Enzyme inhibitor (EI) complex

A
  • Formed transiently

- Easily dissociates in regard to reversible enzyme inhibitors

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3
Q

Chemotherapies

A
  • Function as reversible inhibitors of specific enzymes
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4
Q

Competitive inhibitors

A
  • Try to bind to the same binding site on the enzyme molecule as the substrate
  • Must resemble the enzyme’s natural substrate structurally
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5
Q

At low [S]

A
  • Enzyme will tend to bind to the inhibitor
  • Forms EI complex
  • No catalysis
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6
Q

At high [S]

A
  • Enzyme will bind substrate

- Effect of inhibitor will be minimal

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7
Q

In the presence of large amounts of substrate

A
  • The effect of the inhibitor can be reversed and a genuine Vmax can be attained
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8
Q

In the presence of a competitive inhibitor

A
  • The M/M constant (Km) increases by an amount ( 1 + 1/[Ki]) and 1/Km decreases
  • Km increases
  • 1/Km decreases
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9
Q

The slope of LWB

A
  • Increased by a factor of 1 + [I]/Ki in the presence of a competitive inhibitor
  • No change in Vmax
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10
Q

Non-competitive inhibitor

A
  • Can interact with the enzyme or the ES complex with equal affinity to form EI or ESI complexes
  • Both EI and ESI are catalytically inactive
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11
Q

Increasing substrate concentration with NCI

A
  • No effect on the ability of the inhibitor to reduce reaction rate
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12
Q

Km in NCI

A
  • Not altered in the presence of non-competitive inhibitor

- Vmax is reduced

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13
Q

Drugs as competitive inhibitors

A
  • Antiviral
  • Antibacterial
  • Antitumor
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14
Q

Sulfonamides

A
  • Bacteriostatic agents that resemble the p-aminobenzoic acid (PABA) utilized by bacteria in the synthesis of folic acid
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15
Q

Sulfanomide binding

A
  • Binds to active site the enzyme dihydropteroate synthetase
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16
Q

Most anticancer agents are competitive inhibitors of these

A
  • Thimydylate synthase

- Dihydrofolate reductase

17
Q

Anticancer agents

A
  • Often structurally resemble nitrogenous bases of nucleotides
  • Able to inhibit DNA replication and cellular proliferation
18
Q

Methotrexate (aminopterin)

A
  • Competitive, almost irreversible inhibitor of dihydrofolate reductase
  • Binds with dihydrofolate reductase with greater affinity than its natural substrate
19
Q

Methotrexate usage

A
  • Used effectively as a treatment for childhood leukemia

- Low doses: treats rheumatoid arthritis

20
Q

3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA)

A
  • Competitively inhibits the *** reductase enzyme that catalyzes the rate-limiting step in cholesterol biosynthesis
  • Effective in reducing circulating LDL-cholesterol levels
21
Q

Inhibiting HMG-CoA reductase activity in the liver

A
  • The organ’s demand for cholesterol is increased
  • Up regulates LDL receptor gene expression
  • Increased clearance of plasma LDL
22
Q

Angiotensin I-converting enzyme (ACE) inhibitors

A
  • Reduce the production of angiotensin II form angiotensin I by the angiotensin converting enzyme of endothelial cells
23
Q

Angiotensin II

A
  • Stimulates secretion of aldosterone

- Promotes vasoconstriction of arterioles

24
Q

Chemotherapies as NCIs

A
  • Doxycycline

- Allopurinol

25
Q

Doxycycline

A
  • Broad-spectrum, semi-synthetic tetracycline antibiotic

- Used for treatment of multiple conditions caused by bacteria (acne, chlamydia, lyme disease, etc.)

26
Q

Allopurinol at low concentrations

A
  • Acts as a competitive inhibitor of xanthine oxidase
27
Q

Allopurinol at high concentrations

A
  • Functions as a non-competitive inhibitor
28
Q

Alloxanthine (oxypurinol)

A
  • Allopurinol is converted to this by the xanthine oxidase enzyme and this product is a non-competitive, long lasting inhibitor of the enzyme
29
Q

Xanthine oxidase

A
  • Converts allopurinol to xanthine oxidase

- Commits catalytic suicide converting the pro-drug to the active inhibitor

30
Q

Reversible inhibitors

A
  • Associate with the enzyme molecule non-covalently to reduce reaction rate
  • Structure of enzyme is not altered
  • Can readily dissociate
31
Q

In the presence of a competitive inhibitor (M/M)

A
  • Km increases

- Vmax unchanged

32
Q

In the presence of a non-competitive inhibitor (M/M)

A
  • Km unchanged

- Vmax reduced

33
Q

Allopurinol

A
  • Both a competitive and non-competitive inhibitor of xanthine-oxidase depending on concentration

Biochemistry I (34 decks)

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