Chapter 8 Enzymes

Front 1

trypsin and thrombin specificity

Back 1

Trypsin--must have Lys or Arg side chain
Thrombin--must have Arg side chain

Front 2

apoenzyme

Back 2

free form of an enzyme that uses a cofactor

Front 3

holoenzyme

Back 3

apoenzyme plus cofactor

Front 4

coenzymes

Back 4

mostly small molecules derived from amino acids

Front 5

larger Keq=_________change in energy

Back 5

more negative

Front 6

cofactor of cytP450

Back 6

heme

Front 7

active site residues are usually made up of______________ residues

Back 7

noncontiguous

Front 8

Emil Fisher

Back 8

lock and key

Front 9

Dan Koshland

Back 9

induced fit

Front 10

Michaelis Menten kinetics

Back 10

assumes [S]>>[E]
stability of ES is defined by KM=(Ksub-1 + Ksub2)/Ksub1

Front 11

Michaelis Menten equation

Back 11

Vo=Vmax*([S]/([S]+Km))

Front 12

Lineweaver-Burk Plot

Back 12

1/Vo=1/Vmax+Km/Vmax*1/[S]
end up with straight line instead of hyperbolic
y intercept=Vmax
x intercept=km

Front 13

Km=dissociation constant (Kd) only when

Back 13

ksub2<<ksub-1

Front 14

Ksub2 is the same as

Back 14

Kcat (turnover number or max)--how fast when saturated with substrate

Front 15

Kcat can never be

Back 15

>Ksub1 because Ksub1 is the association constant

Front 16

allosteric enzymes

Back 16

don't follow Michaelis Menten kinetcs--the binding of one substrate can alter other active sites

Front 17

Kcat/Km

Back 17

catalytic efficiency allows a comparison of different enzymes or substrates

Front 18

example of a multi-substrate ordered sequential reaction

Back 18

lactate dehydrogenase--NADH must bind then pyruvate must bind the lactate is released then NAD+ is released

Front 19

example of multi-substrate random sequential reaction

Back 19

creatine kinase--ATP or creatine can bind first and phosphocreatine or ADP can be released first

Front 20

example of multi-substrate double displacement reaction

Back 20

aspartate aminotransferase--aspartate binds, enzyme retains NH3 and oxaloacetate is released, alpha-ketoglutarate binds and glutamate is released (with NH3 bound to it)

Front 21

RNA enzymes

Back 21

ribosymes

Front 22

competitive inhibitors

Back 22

compete for active sites
km changes, but no Vmax

Front 23

uncompetitive inhibitors

Back 23

binds after substrate has bound--next to active site
decreases apparent Vmax and Km

Front 24

Ki

Back 24

=[E][I]/[EI]; dissociation constant for inhibitor--small Ki mean potent inhibitor

Front 25

noncompetitive inhibitor

Back 25

binds not at the active site
decreases Vmax but not Km

Front 26

irreversible inhibitors

Back 26

modify enzymes by formation of new covalent bonds

Front 27

2 examples of group specific reagents

Back 27

DIPF forms covalent bond with OH on serine residue (acetylcholinesterase=enzyme)
iodoacetamide binds covalently to S in Cysteine

Front 28

affinity labels

Back 28

aka reactive substrate analogs
molecules that are structurally similar to substrate for enzyme and covalently bind to active-site residues

Front 29

group specific reagents

Back 29

react with specific side chains of amino acids

Front 30

example of affinity label

Back 30

TPCK inhibits chymotrypsin by binding at active site and reacting irreversibly with His residue

Front 31

suicide inhibitors

Back 31

aka mechanism-based inhibitors--inhibitor binds to enzyme and is initially processed by normal catalytic mechanism--this generates a chemically reactive intermediate that inactivates enzyme through covalent modification

Front 32

example of suicide inhibitor

Back 32

N, N-dimethylpropargylamine inhibits MAO

Front 33

treatment for parkinsons and depression

Back 33

(-) deprenyl (MAO inhibitor)

Front 34

transition state analogs

Back 34

compounds resembling transition state of a catalyzed reaction inhibit enzymes

Front 35

example of transition-state analog

Back 35

pyrrole 2-carboxylic acid binds to proline racemase (changes L-Proline to D-Proline). Transition state of Pro is trigonal as is pyrrole 2-carboxylic acid--binds 160 times more tightly than Pro

Front 36

peptidoglycan

Back 36

cell-wall macromolecule of bacteria--consists of linear polysaccharide chains that are cross-linked by short peptides

Front 37

glycopeptide transpeptidase

Back 37

catalyzes final step in peptidoglycan synthesis--amino group at one end of pentaglycine chain attacks peptide bond between 2 D-alanine residues in another peptide unit forming a peptide bond between glycine and on D-alanine residue (other is released)

Front 38

penicillin

Back 38

inhibits glycopeptide transpeptidase--binds ot active site because it mimics D-Ala-D-Ala moiety of normal substrate--then forms covalent bond with serine residue at active site (penicillin has highly strained 4-membered ring makes it reactive)

Front 39

6 major categories of enzymes

Back 39

oxidoreductases
tranferases
hydrolases
lyases
isomerases
ligases

Front 40

oxidoreductase

Back 40

oxidation-reduction reactions

Front 41

trasnferases

Back 41

group transfer

Front 42

hydrolases

Back 42

hydrolysis reactions (transfer of functional groups to water)

Front 43

lyases

Back 43

addition or removal of groups to form dbl bonds

Front 44

isomerases

Back 44

isomerization (intramolecular group transfer)

Front 45

ligases

Back 45

ligation of 2 substrates at the expense of ATP hydrolysis