# Enzyme Kinetics Flashcards

1
Q

In the Michaelis-Menten Kinetcs, the ___ is always rate limiting step

A

k2/kcat

2
Q

Enzyme kinetics are important for:

A
1. Drug design
2. Drug interactions
3. Toxins (making anti-toxins)
3
Q

In enzyme kinetcs catalyzed reactions, the stubstrate:

A

will be used up until equilibrium is attained

4
Q

In the very beginning there is a very ____relationship

A

linear

5
Q

As substrate comes ____, product goes ____

A

down; up

6
Q

What is going on during pre-steady state

A

concentration of ES is building up

7
Q

What is going on during the steady state

A

After pre steady state, concentration of ES and any other intermediates reaches point where concentrations are approx constant,

8
Q

What is the steady state kinetics experiment like

A
1. Set up several reactions
2. [E] same in each
3. Different substrate conc.
4. Plot amount of P formed against time
5. Measure velocity
9
Q

What does the michaelis menten equation describe

A

the curve obtained by plotting Vo, initial velocity against [S], the substrate concentration

10
Q

What is Km

A

The michaelis menten constant which is the substrate concentration at which Vo= 1/2 Vmax

11
Q

When substrate concentration is much less than Vmax, what kind of relationship do you get

A

linear= 1st order kinetics

12
Q

When substrate concentration is much higher than Km:

A

The eqn reduces to Vo=Vmax; adding more substrate doesnt make a difference. This is called 0 order kinetics.

13
Q

What is the lineweaver-burk equation

A

Transforms michaelis menten equation into equation that gives a straight line plot

14
Q

What is the slope = to in a lineweaver burk plot

A

Km/Vmax

15
Q

What does Km depend on

A
1. Substrate used
2. pH
3. Temperature
16
Q

Hexokinase is the first enzyme in

A

glycolysis; phosphoralates glucose

17
Q

What does Km mean

A

Can be used to calculate the fraction of active sites filled at any substrate concentration

18
Q

Km is related to the rate constants of each step in the ____reaction

A

catalytic

19
Q

WHat is Kd

A

the dissociation constant for the ES complex; provides a measure of the affinity of the enzyme for its substrate.

20
Q

Another way to describe kcat is that it is the:

A

turnover constant=number of substrate molecules converted to product per unit time by a single enzyme molecule saturated with substrate.

21
Q

What is catalytic efficiency = to

A

the factor kcat/km

22
Q

What are two broad classes of enzyme inhibitors

A
1. Reversible

2. Irreversible

23
Q

Aspirin inhibits which enzyme

A

cylooxygenase; which is used for inflammation/pain

24
Q

ACE inhibits which enzyme

A

angiotensin converting enzyme; which then dec blood pressure

25
Q

Statins inhibit which enzyme

A

HMGCoA reductase; lowers cholestrol

26
Q

Simbrinza inhibis which enzyme

A

Carbonic anhydrase; glaucoma

27
Q

What are the three types of reversible inhibitors

A
1. competitive
2. uncompetitive
3. mixed inhibition (non-competitive)
28
Q

What is a competitive inhibitor

A

a compound that resembles a normal substrate; competes with substrate for binding to active site but no reaction occurs when bound.

29
Q

What does a compettive inhibitor curve look like

A

Vmax doesnt change, just takes more substrate to get there. Km (increases) and slope changes.

30
Q

What is DIFP

A

An irreversible inhibitor; it combines with reactive serine 195 and makes a covalent bond and just sits there. Doesnt come off

31
Q

What are target enzymes for DIFP

A
1. Acetylcholinesterase

2. Chymotrypsin

32
Q

What is penicillin

A

An irreversible inhibitor; once bound in active site, beta lactam ring covalently reacts with active site serine (enzyme activity irreversibly destroyed)

33
Q

What are suicide inhibitors

A

Special class of irreversible inhibitor. Bind to active site and begin to participate in normal enzyme reactions. Form an intermediate that is covalently bound to an active site reactive group as a normal step in reaction. Do not undergo further steps

34
Q

What is an ex of a suicide inhibitor

A

Flourouracil: impt chemotherapeutic agent in cancer treatment that targets production of DNA precursors.

35
Q

What are the four major mechanisms of regulation of enzyme activity

A
1. Stimulation and inhibition by control proteins.
2. Reversible covalent modification
3. Proteolytic activation
4. Allosterism
36
Q

Neutrophils are

A

the first cells that arrive and invade foreigners. Break down ECM in area.

37
Q

What is alpha 1 antitrypsin

A

potent elastase inhibitor; binds strongly, blocks active site – deficiency causes emphysema (CT in lung damaged)

38
Q

What is elastase

A

released by neutrophils responding to bacterial infection; degrades collagen and elastin

39
Q

What is reversible covalent modification

A

reversible attachment of small functional group. Often phosphoryl group. Alters activiy: enzymes in glycogen metabolism

40
Q

WHat is proteolytic activation

A

Zymogen: inactive precursor of enzyme; irreversibly activated by proteolytic cleavage of one or more peptide bonds.

41
Q

What are examples of proteolytic activation

A

blood clotting enzymes, digestive enzymes, angiotensin II

42
Q

Kinases

A

phosphoralates things

43
Q

What is allosterism

A

A change in the conformation and as a result activity - of an enzyme resulting from the binding of a compound at a site on the enzyme other than the active binding site.

44
Q

What is a modulator (effector)

A

regulatory metabolite that modulates enzyme activity, usually by reversible, non covalent binding

45
Q

Allosteric enzymes show ____rate curves

A

46
Q

Positive modulators ____substrate affinity

A

increase

47
Q

Negative modulators (inhibitors)____substrate affinity

A

decrease

48
Q

Sigmoidal substrate activity curves are consistent with subunits exhibiting

A

cooperativity (hemoglobin)

49
Q

WHat is cooperativity

A

The influence of the binding of a ligand to one subunit on the binding of a ligand to a second subunit; usually involves conformational change

50
Q

What are the two observations that the models for allosterism explain?

A
1. Sigmoidal curve with substrate alone (no modulators)

2. Change in curve in response to positive and negative modulators

51
Q

What are the two models of allosterism

A
1. Concerted (symmetry) model

2. Sequential model

52
Q

What does the concerted/symmetry model propose

A

an allosteric enzyme molecule can exist in only two states:

1. Tense state
2. Relaxed state
53
Q

What is relaxed state

A

All subunits are in active or high affinity state

54
Q

What is tense state

A

all subunits are in inactive or low affinity state

55
Q

What is an activator:

A

Binds to R form, shifting equilibrium and increasing substrate binding

56
Q

What is an inhibitor

A

Binds preferentially to T form, shifting equiliubrium, decerases substate binding

57
Q

What is the sequential model

A

Binding of ligand to any one subunit causes a conformational change in that subunit; change partially transmitted to one or more adjacent subunits.

58
Q

What is activator binding

A

causes conformational change to increase subunit affinity for substrate or can increase effect transmitted by subunit

59
Q

What is inhibitor binding

A

Causes conformational change to decrease subunit affinity for substrate or can dec effect transmitted by subunit.

60
Q

The best example of allosteric regulation is:

A

hemoglobin