Properties of Enzymes Flashcards Preview

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Flashcards in Properties of Enzymes Deck (27):
1

Catalysts

Increase the rate that equilibrium is reached by lowering the activation energy for a process

2

Substrate

What an enzyme acts on

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Oxidoreductases

Class of enzymes
Catalyze oxidation-reduction reactions
Usually require a coenzyme like NAD+ or NADP+

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Coenzyme

Molecules that supply enzymes with additional functional groups needed for reactions

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Transferases

Class of enzymes
Catalyze functional group-transfer reactions
May require coenzymes

6

Hydrolases

Class of enzymes
Catalyze hydrolysis of bonds

7

Lyases

Class of enzymes
Catalyze lysis of a substrate (elimination reactions)

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Synthases

Lyases that catalyze addition reactions

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Isomerases

Class of enzymes
Catalyze interconversion between isomers

10

Ligases

Class of enzymes
Catalyze joining of 2 substrates
Often require energy from ATP to drive reaction

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Initial velocity of enzymatic reaction

Vo= k2 [ES]

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Steady-state approximation

Period of time (usually at the beginning of a reaction) where the ES complex is formed at the same rate as it decomposes, so that there is no net change in the [ES]

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Michaelis-Menten equation

Vo=k2[ES]=(Vmax[S])/(Km+[S])

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kcat (catalytic constant)

kcat= (moles of substrate -> product)/[(second)(moles of enzyme)]
Vmax= kcat[E total]

15

Km (Michaelis constant)

Measure of affinity of the enzyme for the substrate
Km=[S]=0.5Vmax

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Catalytic proficiency

Effectiveness of an enzyme

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Lineweaver-Burke plot

Plot 1/Vo (y-axis) vs. 1/[S] (x-axis)
Y-intercept is 1/Vmax
X-intercept is -1/Km

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Inhibitor

Compound that binds to an enzyme and interferes with its activity

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Reversible inhibitor

Binds enzyme via noncovalent forces

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Irreversible inhibitor

Binds enzyme covalently
"Kills" enzyme
Example: organophosphorus inhibitors (sarin: nerve gas)

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Competitive inhibitor

Most common mode of enzyme inhibition
Binds free enzyme molecule only
Competes with substrate for binding
Doesn't affect Vmax
Raises Km

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Uncompetitive inhibitor

Binds ES complex (not free enzyme)
Usually only occurs with multisubstrate reactions
Lowers both Vmax and Km

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Noncompetitive inhibitor

Can bind to enzyme or ES complex
Don't bind at same site as substrate
Decreases Vmax
Doesn't affect Km

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Affinity labels

Irreversible inhibitors with affinity for an enzyme's active site
Useful in determining which residues are critical for enzymatic activity or are proximal to substrate binding

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Allosteric enzymes

Don't follow Michaelis-Menten kinetics (sigmoidal plot instead of line)
Enzymatic activities are changed by metabolic activators and inhibitors (molecules that don't resemble substrates or products)
Exhibit cooperativity

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Regulation by covalent modification

Method of controlling enzyme activity through phosphorylation
More permanent that allosteric modification, but can be reversible

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6 categories of enzymes

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases