Chapter 12: Enzyme Kinetics, Inhibition, and Control

Question 1

Indicates the Progress of a Reaction as a Function of Time

Answer 1

A Rate Equation

Question 2

occurs at high substrate concentrations when the enzyme is saturated

Answer 2

maximal velocity of a reaction, Vmax

Question 3

is a measure of the affinity of the enzyme for its substrate

Answer 3

Km

Question 4

another name for catalytic constant (kcat)

Answer 4

turnover number

Question 5

the maximal number of molecules of substrate converted to product per active site per unit time of several different substrates to different products

Answer 5

catalytic constant (kcat)

Question 6

a measure of an enzyme’s catalytic efficiency

Answer 6

kcat/Km

Question 7

A better method for determining the values of Vmax and KM is

Answer 7

is Lineweaver–Burk or
double-reciprocal plot.

Question 8

Most enzymatic reactions requiring multiple substrates and yielding multiple products

Answer 8

bisubstrate reactions

Question 9

Reactions in which all substrates must combine with the enzyme before a reaction can occur and products be released are known as

Answer 9

sequential reactions.

Question 10

Many NAD+ and NADP+ requiring dehydrogenases follow an what?

Answer 10

Ordered bisubstrate reaction

Question 11

Some dehydrogenases and kinases operate through

Answer 11

random bisubstrate reaction

Question 12

Group-transfer reactions in which one or more products are released before all substrates have been added are known as

Answer 12

Ping Pong reactions

Question 13

In Ping Pong reactions, the substrates A and B do not what

Answer 13

encounter one another on the surface of the enzyme.

Question 14

what enzymes react with Ping Pong
mechanisms

Answer 14

trypsin, transaminases, and some flavoenzymes

Question 15

Substances that reduce an
enzyme’s activity in this way are known as

Answer 15

inhibitors

Question 15

A substance that competes directly with a normal substrate for an enzyme’s substrate-binding site is known as a

Answer 15

competitive inhibitor.

Question 16

are particularly effective inhibitors.

Answer 16

Transition state analogs

Question 17

a citric acid cycle enzyme that converts succinate to fumarate,

Answer 17

succinate dehydrogenase

Question 18

what inhibits succinate dehydrogenase

Answer 18

malonate

Question 19

reduces the conc of free enzyme available for substrate binding.

Answer 19

A competitive inhibitor

Question 20

what can overwhelm a competitive inhibitor.

Answer 20

concentration of substrate

Question 21

significantly limits the production of the flu virus as a competitive inhibitor of influenza neuraminidase when is hydrolyzed to oseltamivir carboxylate in the liver

Answer 21

Tamiflu

Question 21

hydrolyzes sialic acids of membrane
glycoproteins to help the viral particles escape from the host cell surface.

Answer 21

Neuraminidase

Question 22

Comparing the KI values of competitive inhibitors with different structures can provide information
about what

Answer 22

the binding properties of an enzyme’s active site and hence its catalytic mechanism.

Question 23

is the principle behind the use of ethanol to treat methanol poisoning

Answer 23

Competitive inhibition

Question 24

are competitive inhibitors of dihydrofolate reductase.

Answer 24

Methotrexate and Trimethoprim

Question 25

is used for cancer
chemotherapy

Answer 25

Methotrexate

Question 26

is an effective antibiotic because it binds to bacterial dihydrofolate reductase nearly 100,000 times better than to the mammalian enzyme. It is used to treat certain urinary and middle ear bacterial infections

Answer 26

Trimethoprim

Question 27

which need not resemble substrate, presumably distorts the active site, thereby rendering the enzyme catalytically inactive.

Answer 27

The binding of uncompetitive inhibitor

Question 28

binds to enzyme sites that participate in both substrate binding and catalysis.

Answer 28

a mixed inhibitor

Question 29

If the enzyme and enzyme–substrate complex bind I with equal affinity, then only Vmax is affected, a phenomenon that is named

Answer 29

pure noncompetitive inhibition.

Question 30

does substrate binding reverse the effects of mixed inhibition

Answer 30

no

Question 31

are non-competitive inhibitors of reverse transcriptase so they have been used to control HIV levels in AIDS.

Answer 31

Nevirapine or Delavirdine

Question 32

is an uncompetitive and specific inhibitor of Type II 5-reductase, an enzyme that converts testosterone into dihydrotestosterone.

Answer 32

Finasteride

Question 33

is believed to bind to the NADH cofactor of the enzyme.

Answer 33

Finasteride

Question 34

how to control Enzyme availability

Answer 34

rates of synthesis and its rate of degradation controlled by the cell and is subject to dramatic changes over time spans

Question 35

The amount of a given enzyme in a cell depends

Answer 35

rate of synthesis and its rate of degradation

Question 36

can be directly controlled
through structural alterations that influence the enzyme’s substrate-binding affinity or turnover number

Answer 36

An enzyme’s catalytic activity

Question 37

can cause large changes in enzymatic activity.

Answer 37

Allosteric mechanisms

Question 38

ATCase is allosterically inhibited by

Answer 38

cytidine triphosphate (CTP)

Question 39

it inhibits an earlier step in its own biosynthesis.

Answer 39

feedback inhibitor

Question 40

allosterically reduce the activity of the catalytic subunits in the intact enzyme

Answer 40

The regulatory subunits

Question 41

The most common covalent modification

Answer 41

reversible phosphorylation and dephosphorylation (the
attachment and removal of a phosphoryl group) of the hydroxyl group of a Ser, Thr, or T yr residue.

Question 42

an important supplier of fuel for metabolic activities

Answer 42

glycogen breakdown

Question 43

This is the rate-controlling step in the
metabolic pathway of glycogen breakdown

Answer 43

lycogen phosphorylase catalyzes the
phosphorolysis of glycogen to yield glucose-1-phosphate (G1P).

Question 44

catalytically and structurally similar but genetically distinct enzymes from
the same organism;

Answer 44

isozymes also called isoforms

Question 45

is regulated both by
allosteric interactions and by
phosphorylation/dephosphorylation.

Answer 45

Muscle glycogen phosphorylase

Question 46

the phosphorylated
form of the enzyme

Answer 46

phosphorylase alpha

Question 47

The dephospho form is called

Answer 47

phosphorylase beta

Question 48

is inactive because it has a malformed active site and a surface loop that blocks substrate access to its binding site.

Answer 48

T -state enzyme

Question 49

is allosterically controlled by the effectors AMP,A TP , and G6P and is mostly in the T state under
physiological conditions.

Answer 49

phosphorylase beta

Question 50

is unresponsive to these
effectors and is mostly in the

Answer 50

phosphorylase alpha

Question 51

A drug candidate that exhibits a desired effect is called a

Answer 51

lead compound

Question 52

what makes a good lead compound

Answer 52

binds to its target protein with a dissociation constant (for an enzyme, an inhibition constant) of less than 1 μM. Such a high affinity is necessary to minimize a drug’s less specific binding to other macromolecules in the body and to ensure that only low doses of the drug need be taken

Question 53

Even minor modifications to a drug candidate can result in what?

Answer 53

major changes in its pharmacological properties

Question 54

uses the structure of a receptor or enzyme in complex with a drug candidate to guide the development of more efficacious compounds

Answer 54

Structure-based drug design (also called rational drug design

Question 55

is the discipline within clinical pharmacology that broadly describes the changes in the quantity of drug and/or drug metabolite in various body compartments over time

Answer 55

pharmacokinetics

Question 56

The most effective drugs are usually a compromise meaning

Answer 56

they are neither too
lipophilic nor too hydrophilic