1
Chapter 21 -1
Chapter 21
Enzymes & Vitamins
What are enzymes and what do they do?
Most enzymes are___________________
Recall energy profiles for reactions, what do they
look like with and without a catalyst?
2
Chapter 21 -2
How fast are biochemical reactions catalyzed by
enzymes?
catalase
2H2O2
2_____ + ____
Reaction occurs 40 ________ times every second
Naming Enzymes
Common names:
substrate — ??? + ase = name
e.g.
Urea
Lactose
Sucrose
Or
function + ase = name
e.g.
The protein that removes H atoms =
The protein that adds O atoms =
3
Chapter 21 -3
Kind names: gives both substrate and function
e.g.
lactate dehydrogenase
pyruvate decarboxylase
___kind names: ____________________________
e.g.
chymotrypsin
and trypsin
Classification of Enzymes
International Commission on Enzymes
____ general types of reactions catalyzed (Table
21.1)
1.
Oxidoreductases
e.g. Dehydrogenases in the following reaction
NAD
NADH
+H +
CH3 CH2 OH
NAD
O
CH3 C H
O
CH3 C H
NADH
+H +
O
CH3 C OH
4
Chapter 21 -4
2.
Transferases e.g. Alanine transaminase
O O
O
-O C C CH2 CH2 C O
α-ketoglutarate
+
NH3 O
CH3 CH C
alanine
O O
O
CH3 C C O
pyruvate
+
O NH3
O
-O C CH CH2 CH2 C O
glutamate
Is glutamic acid an _____________ amino acid?
5
Chapter 21 -5
3.
Hydrolases
Amylase
e.g. Chymotrypsin or
O
O
N CH C
H CH
2
N CH C
H
CH3
H2O
O
N CH C O
H CH
2
O
+
H3N CH C
CH3
What is the bond being broken in a hydrolysis
reaction catalyzed by amylase?
6
Chapter 21 -6
4.
Lyases
e.g. Pyruvate decarboxylase
O O
H+
O
CH3 C H
CH3 C C O
pyruvate
CO 2
5.
Isomerase
e.g. Maleate isomerase
COO-
-OOC
H
H
?
H
-OOC
COO-
H
?
7
Chapter 21 -7
6.
Ligases
e.g. Pyruvate carboxylase
O O
CH3 C C O
pyruvate
CO 2
+
ATP
ADP + Pi + H +
O
O O
O C CH2 C C O
oxaloacetate
Types of Enzyme Specificity
Type
Reaction
Example
_________
one type of reaction,
single substrate
urease
_________
one type of reaction,
similar substrates
hexokinase
_________
one type of reaction,
specific type of bond
trpsin
How can enzymes be so specific?
8
Chapter 21 -8
The Enzyme Active Site
The Place
O
O
+
H3C C N CH C O
H CH
2
H3N CH C O
CH2
O
O
H3C C S-CoA
HO
HO
OH
OH
O
H3N CH C O
CH2
+
O
+
+
H3N CH C O
H3N CH2
CH2
CH2
HO
OH
OH
O
O
+
O
+
+
H3N CH C O
H3N CH C O
H3N CH C O
CH2
CH2
CH2
N-H
N-H
HO
N-H
CH3O
9
Chapter 21 -9
Mechanistic Models of Enzyme Catalysis
1) Lock-and-Key Model
Lock
key
Enzyme-substrate
Complex
Doesn’t explain the group specificity type of
reactions
2) Induced Fit Model
Active site
substrate
Enzyme-substrate
Complex
10
Chapter 21 -10
What about “Non-fitting substrates” ??
Active site
substrate
______________
No __________________, No __________________.
What about “Fitting but non-reactive substrates??
Enzyme Inhibition
1) Reversible
a) Competitive
Structural analogs
compete to bind,
concentration
dependent
versus
b) Non-competitive
weak binding ___________
alters the environment, if
dissociated, enzyme is
recovered (Pb2+,Ag+, etc.)
11
Chapter 21 -11
2) Irreversible (binds very tightly, _______________
to the enzyme, permanently block the active site or
destroy the catalytic ability)
e.g.
acetylcholinesterase inhibitors
O
O
F
e.g.
F
P O
P O
O
O
DFP
Sarin
glycoprotein peptidase
R
N
S
H
O
N
O
COO-
12
Chapter 21 -12
Factors Affecting Enzyme Activity (Reaction Rates)
Temperature
pH
13
Chapter 21 -13
pH Optimum for Different Enzymes
Effect of Enzyme and Substrate Concentrations
Enzyme Concentration ??
14
Chapter 21 -14
Concentration of Substrates ??
15
Chapter 21 -15
Allosteric Enzymes
What are they ??
What are Positive and Negative Regulators ??
What is Feed-Back Control ??
For example, the process of bacterial conversion of
threonine to Isoleucine
In E1, there is a site for ______ to bind and the
binding ________ down the E1 function.
16
Chapter 21 -16
Enzyme Cofactors
Simple enzymes –
Enzymes requires “extra chemistry”:
Metal ions:
Zn2+, Mg2+, Fe2+/ Fe3+, Ni2+
Coenzyme:
- small organic molecules
- sometimes these are
vitamins
17
Chapter 21 -17
The Water-Soluble Vitamins:
B and C
(there are _____ B Vitamins)
The Fat-Soluble Vitamins:
A, D, E, and K
O
H3C
H3C
N
N
N
N
O
O
O
O
CHOH
CHOH
N
CH3
H
Riboflavin
(Vit. B2)
Pyridoxal phosphate
(Vit. B6)
CH2
OH
OH
P O
CH2
CHOH
O
H
H
HO
O
HOCH2
HO
O
OH
Ascorbic Acid
(Vit. C)
18
Chapter 21 -18
H3C
C H3
C H3
C H3
OH
C H3
R etin o l
(V it. A)
H3C
C H3
H2C
P re-V it. D
HO
Things to consider:
1) Bioavailability
2) Stability
3) Solubility
4) Toxicity
19
Chapter 21 -19
The B Vitamins
- Thiamin
- Niacin
- Pantothenic acid
- Folate
- Riboflavin
- Biotin
- Pyridoxine
- Cyanocobalamin
B6
thiamin
folate
niacin
Pantothenic
acid
riboflavin
20
Chapter 21 -20
Vitamin
Best source
Thiamin
lean pork chop
Riboflavin
liver
Niacin
chicken breast
Folate
lentils
B6
banana
B12
only animal source
Pantothenic acid
widespread in foods
Biotin
widespread in foods
Thiamin
easily destroyed by heating, boiling
Riboflavin
easily destroyed by UV light and irradiation
Niacin
fairly heat resistant, but leach into water
Folate
easily destroyed by heat and oxygen
B6
easily destroyed by heating
B12
Inactivated by microwave--use only oven or stove top for
cooking meat and milk products
Pantothenic acid
easily destroyed by freezing, canning, refining processes
21
Chapter 21 -21
Best Meal for Vitamins’ Sake
Thiamin (cold)
Riboflavin
(keep in dark)
Niacin
(less water)
Folate
(raw, fresh c
Thiamin
Riboflavin
B12
Folate
(cold,
air-tight
container)
Thiamin
B6
Niacin
B12
(no microwave)
22
Chapter 21 -22
Vitamin C (Ascorbic Acid)
- deficiency results in scurvy
- involved in the synthesis of collagen
Ascorbic Acid
(Vit. C)
O
H2N
+
O
O
H2N
+
OH
1 cup of orange juice for breakfast
A salad for lunch
Broccoli and potato for dinner
> 300 mg
¾RDA = 75-90 mg
Vit. C is easily destroyed by heat and oxygen
O
23
Chapter 21 -23
Forms of Vitamin A
OH
retinol
H
O
retinal
OH
O
retinoic acid
β-carotene
24
Chapter 21 -24
25
Chapter 21 -25
11-cis-retinal
11-trans-retinal
light
metarhodopsin-II
N
OPSIN
rhodopsin
OPSIN
N
retinal
isomerism
H
O
OPSIN
light
H
O
OPSIN
Vitamin D can be synthesized in the body with
the help of sunlight or obtained from foods
derived from animals. A deficiency causes
rickets in childhood. Fortified Milk is an
important food source.
26
Chapter 21 -26
protein
or
.
.
protein
lipids
(PUFA)
Vit. E
or
+ Vit. E
.
(active)
lipids
(PUFA)
Vit. E
+ Vit. C
+ Vit. E
.
(inactive)
+ Vit. C
(active)
(inactive)
Vitamin E has 3 stereogenic centres
Therefore, when made synthetically:
2 x 2 x 2 = 8 different forms
ONLY 1 is the NATURAL & ACTIVE form
1 / 8th
27
Chapter 21 -27
Notable food sources of vitamin K include:
milk, eggs, brussels sprouts, collards, liver,
cabbage, spinach, and broccoli.
Chemical names:
Vit. K1:
Vit. K2: