Ionic strength pH
TEMPERATURE Shear
Pressure (hydrostatic) Surface tension
Chemicals (alcohol, urea, H
2O
2...) Light, sonication, ionising radiations Reverzible
changes Irreverzible
6. OTHER EFFECTS ON ENZYME ACTIVITY
1
Active side chains
Changes in activity of proteins are caused by changes of ami- no acid side chains.
Acidic: –COOH: Asp, Glu Basic: -NH
2: Lys, Arg (and terminal –COOH and -NH
2)amide: –CO-NH
2: Asn, Gln
Polar: –OH: Ser, Thr -SH: Cys, -S-CH
3: Met Imidazole: His Guanidin: Arg
H-bonds: C=O …… H-O- C=O …… H-NH-
2
Proteins: + and – charged side chains ← their charge de- pends on dissociation ← determined by pH → it effects the active centre.
Recharge of enzyme:
Only E
-is active!
Ratio of active enzymes:
Michaelis-féle pH függvények:
Y-= E-/ E0
Y 1
1 H / K
1K / H
2−
+ +
= + +
Effect of pH
1
2- 2
2 0
H E
K E
H E
K E
E E E E
+ −
+
−
− −
= ⋅
= ⋅
= + +
2
E E H
E E H
− +
− − +
→ +
←
→ +
←
3
Y 1
1 H / K
1K / H
2−
+ +
= + +
Effect of pH
( )
optimum(
1 2)
2 1 optimum
pK 2 pK
pH 1
K K H
+
=
+
=
1
Effect of pH
5
Glutamate-dehydrogenase pepsine
arginase
salivary-amylase
REALTIVE ENZYME ACTIVITY
Effect of pH temperature
Increasing reaction rate Double effect
decrease: denaturation
depends on treatment time, too!
irreversible
reversible
a
a
dE kE
dt = − E
a( ) t = Ea0e
−kt
6
S
d= ~900 KJ/mol.K H
d= 280-310 KJ/mol If:
→
and
Effect of pH temperature
Large: sensitively reacts on small change (one H-bond: 12,5-29,3 kJ/mol)
α= combination of (β,kB,h,E0,∆S*)
Kmalso depends on T!
Kd
a i
E ← → E
∆
− ∆
=
− ∆
=
= R
exp S RT
exp H RT
exp G E K
E
d d dd a i
0 a i
E = E + E
( )
max 2 a
V = k T E
K 1 E E
d 0
a = +
( )
B S /R E/RT2 e e
h T T k
k
* −
∆ ⋅
=β
V Te
1 e e
max
E/ RT S / R* H / RTd
= + ⋅
−
−
α
∆ ∆
7
Effect of pH temperature
pH optimum and stability
9
Temperature optimum and stability
10
A h ő mérséklet hatása
11
