Enzymes are biomolecules that catalyze chemical reactions and increase their rates. They have high catalytic power, increasing reaction rates by factors of 108 to 1020. Enzymes also exhibit specificity, only catalyzing certain reactions and binding specific substrates. Regulation of enzyme activity ensures metabolic reactions proceed at appropriate rates. Enzymes were first observed to catalyze reactions in the 1800s and were formally discovered in the late 1800s. They are now classified based on the type of reaction catalyzed and identified by systematic naming conventions.

1. Enzyme classification and properties

2. ENZYMES
Definitions--
 A biomolecule either Protein or RNA, that catalyse a
specific chemical reaction, enhance the rate of a
reaction by providing a reaction path with a lower
activation energy

3. Fundamental Properties
1) Catalytic power-speeding up reactions 108 to 1020 fold.
They speed up reactions without being
used up.
2) Specificity
a) for substrate - ranges from absolute to relative
b) for reaction catalyzed
3) Regulated-- some enzymes can sense metabolic
signals.

4. Catalytic Power
Catalytic Power is defined as the Ratio of the Enzyme-
Catalyzed Rate of a Reaction to the Uncatalyzed
Rate
e.g. Urease-
 At 20°C, the rate constant for the enzyme-catalyzed
reaction is 3 X 104/sec
 the rate constant for the uncatalyzed hydrolysis of
urea is 3 X 1010/sec
 1014 is the ratio of the catalyzed rate to the
uncatalyzed rate of reaction

5. Specificity
Defined as the Selectivity of Enzymes for the
Reactants Upon which They Act
In an enzyme-catalyzed reaction, none of the substrate
is diverted into nonproductive side reactions, so no
wasteful by-products are produced.

6. The substances upon which an enzyme acts are traditionally
called- substrates
The selective qualities of an enzyme are collectively
recognized- specificity
The specific site on the enzyme where substrate binds and
catalysis occurs is called- active site

7. Regulation
Regulation of Enzyme Activity Ensures That the Rate of
Metabolic Reactions Is Appropriate to Cellular
Requirements
 essential to the integration and regulation of metabolism
Achieved by various ways
 Inhibitor
 Activator
 Hormonal
 Rate of synthesis

8. History
 As early as the late 1700s and early 1800s, the digestion
of meat by stomach secretions and the conversion of
starch to sugars by plant extracts and saliva were known.
However, the mechanism by which this occurred had not
been identified

9.  In the 19th century, when studying the fermentation of
sugar to alcohol by yeast, Louis Pasteur came to the
conclusion that this fermentation was catalyzed by a
vital force contained within the yeast cells called
"ferments", which were thought to function only within
living organisms. He wrote that "alcoholic fermentation
is an act correlated with the life and organization of the
yeast cells, not with the death or putrefaction of the
cells.

10.  In 1878 German physiologist Wilhelm Kühne (1837–1900) first used
the term enzyme. The word enzyme was used later to refer to
nonliving substances such as pepsin, and the word ferment used to
refer to chemical activity produced by living organisms
 In 1897 Eduard Buchner began to study the ability of yeast extracts
that lacked any living yeast cells to ferment sugar. In a series of
experiments at the University of Berlin, he found that the sugar was
fermented even when there were no living yeast cells in the mixture
 He named the enzyme that brought about the fermentation of
sucrose "zymase". In 1907 he received the Nobel Prize in
Chemistry“ for his biochemical research and his discovery of cell-
free fermentation"

11. Classification and Nomenclature
1. Often named by adding the suffix -ase to the name of the
substrate upon which they acted
e.g. Urease, DNA Polymerase

12. 2. Names bearing little resemblance to their activity
e.g. catalase - the peroxide-decomposing enzyme
Proteolytic enzymes (proteases) of the digestive tract
Trypsin- Gr. Word Tryein means to wear down
Pepsin- Pepsis means digestion

13. IUB nomemclature
1956 - to create a systematic basis for enzyme
nomenclature
 4 digit numbered code
 first digit - major class
 Second digit - sub class
 third digit - sub sub class
 final digit - specific enzyme

14. 2.7.1.1
ATP: glucose phosphotransferase
2- class name (transferase)
7- subclass name (phosphotransferase)
1- sub sub class (hydroxyl group as acceptor)
1- specific enzyme (D- glucose as phosphoryl group
acceptor)

15. Enzyme classification
 Six classes
1. Oxidoreductase- transfer of reducing equivalents from
one redox system to another
e.g. Alcohol Dehydrogenase
Lactate dehydrogenase
cytochrome oxidase

16. 2. Transferase
functional group is transferred from one compound to
another
e.g. kinases
transaminase
phosphorylase

17. 3. Hydrolase
cleave C-O, C-N, C-S or P-O etc bonds by adding water
across the bond
e.g. lipase
acid phosphatase
(important in digestive process)

18. 4. Lyases
cleave C-O, C-N, or C-S bonds but do so without addition
of water and without oxidizing or reducing the substrates
e.g. aldolase
fumarase
Carbonic anhydrase

19. 5. Isomerase
catalyze intramolecular rearrangements of functional groups
that reversibly interconvert to optical or geometric
isomers
e.g. Triose isomerase
phosphohexose isomerase
mutase

20. 6. Ligase
catalyze biosynthetic reactions that form a covalent bond
between two substrates utilizing ATP-ADP
interconversion
e.g. glutamine synthetase
DNA- ligase

21. Specificity
highly specific compared to other catalyst
catalyzes only specific reaction
3 types
1. Stereospecificity/ optical specificity
2. Reaction specificity
3. Substrate specificity

22. Optical specificity
 able to recognise optical isomers of the substrate
 Act only on one isomer
e.g. enzymes of amino acid metabolism (D & L Amino acid
oxidase)
Isomerase do not exhibit stereospecificity

23. Reaction Specificity
 catalyze only one specific reaction over substrate
e.g. amino acid can undergo deamination, transamination,
decarboxylation and each is catalysed by separate enzyme

24. Substrate specificity
specific towards their substrates
e.g. glucokinase and galactokinase- both transfer phophoryl
group from ATP to different molecule
3 types
a. Absolute
b. Relative substrate
c. broad

25. Absolute substrate specificity
 Act only on one substrate
e.g. urease

26. Relative substrate specificity
act on structurally related substrates
Further divide into
i. Group dependent- act on specific group e.g. trypsin-
break peptide bond between lysine and arginine,
Chymotripsin act on aromatic AA
ii. Bond specificity- act on specific bond e.g. proteolytic
enzyme, glycosidase

27. Broad specificity
 Act on closely related substrates
e.g. hexokinase- act on many hexoses

28. Chemical Nature & Properties of Enzyme
 Protein or RNA
 Tertiary structure and specific conformation- essential for
catalytic power
 Holoenzyme- functional unit
 Apoenzyme & coenzyme

29. Prosthetic group Coenzyme/cofactor
Non protein molecule Non protein molecule
Tightly (covalently)
bound
Loosely bound
Stable incorporation Dissociable
Cannot be dissociated Seperable by dialysis
etc

30. Monomeric Enzyme- made of a single polypeptide e.g.
ribonuclease, trypsin
Oligomeric Enzyme- more than one polypeptide e.g.
LDH, aspartate carbamoylase
Multienzyme complex- specific sites to catalyse
different reactions in sequence. Only native
conformation is active not individual e.g. pyruvate
dehydrogenase

31. Multienzyme Complexes and
Multifunctional Enzymes
 In a number of metabolic pathways, several enzymes
which catalyze different stages of the process have
been found to be associated noncovalently, giving a
multienzyme complex.
 Examples: Pyruvate Dehydrogenase Complex; Electron Respiratory
Chain
 In other cases, different activities may be found on a
single multifunctional polypeptide chain. The presence
of multiple activities is on a single polypeptide chain is
usually the result of a gene fusion event