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Introduction
The use of enzymes in the diagnosis of disease is one of the important benefits
derived from the intensive research in biochemistry since the 1940's
Enzymes have provided the basis for the field of clinical chemistry
It is, however, only within the recent past few decades that interest in diagnostic
enzymology has multiplied
Many methods currently on record in the literature are not in wide use, and there are
still large areas of medical research in which the diagnostic potential of enzyme
reactions has not been explored at all
Early Enzyme Discoveries
Some of the earliest studies were performed in 1835 by the Swedish chemist
Jon Jakob Berzelius who termed their chemical action catalytic
It was not until 1926, however, that the first enzyme was obtained in pure form,
a feat accomplished by James B. Sumner of Cornell University
Sumner was able to isolate and crystallize the enzyme urease from the jack
bean. His work was to earn him the 1947 Nobel Prize
John H. Northrop and Wendell M. Stanley of the Rockefeller Institute for
Medical Research shared the 1947 Nobel Prize with Sumner. They discovered
a complex procedure for isolating pepsin.
Enzymes and Life Processes
The living cell is the site of tremendous biochemical activity called
metabolism
This is the process of chemical and physical change which goes on
continually in the living organism
Build-up of new tissue, replacement of old tissue, conversion of food to energy,
disposal of waste materials, reproduction - all the activities that we characterize as
"life".
The greatest majority of these biochemical reactions do not take place
spontaneously
The phenomenon of catalysis makes possible biochemical reactions
necessary for all life processes
Catalysis
Catalysis is defined as the acceleration of a chemical reaction by some
substance which itself undergoes no permanent chemical change
The catalysts of biochemical reactions are enzymes and are responsible for
bringing about almost all of the chemical reactions in living organisms
Without enzymes, these reactions take place at a rate far too slow for the pace of
metabolism
Chemical Nature of Enzymes.
Many enzymes require the presence of other compounds - cofactors - before their
catalytic activity can be exerted.
This entire active complex is referred to as the holoenzyme; i.e., apoenzyme (protein
portion) plus the cofactor (coenzyme, prosthetic group or metal-ion-activator) is
called the holoenzyme.
Apoenzyme + Cofactor = Holoenzyme
.1- A coenzyme - a non-protein organic substance which is dialyzable, thermostable and loosely
attached to the protein part.
.2- A prosthetic group - an organic substance which is dialyzable and thermostable which is firmly
attached to the protein or apoenzyme portion.
.3- A metal-ion-activator - these include K ,+Fe ,++Fe ,++Zn ,++Mg ,++Ca
Specificity of Enzymes
One of the properties of enzymes that makes them so important as diagnostic and
research tools is the specificity they exhibit relative to the reactions they catalyze
Other enzymes will be specific for a particular type of chemical bond or functional group
In general, there are four distinct types of specificity:
A- Absolute specificity - the enzyme will catalyze only one reaction.
B- Group specificity - the enzyme will act only on molecules that have specific
functional groups, such as amino, phosphate and methyl groups.
C- Linkage specificity - the enzyme will act on a particular type of chemical bond
regardless of the rest of the molecular structure.
D- Stereochemical specificity - the enzyme will act on a particular steric or
optical isomer.
Enzymes can be classified by the kind of chemical reaction catalyzed
1- Addition or removal of water
A-Hydrolases - these include esterases, carbohydrases, nucleases, deaminases,
amidases, and proteases
B-Hydrases such as fumarase, enolase, aconitase and carbonic anhydrase
2- Transfer of electrons
A-Oxidases
B-Dehydrogenases
3- Transfer of a radical
A-Transglycosidases - of monosaccharides
B-Transphosphorylases and phosphomutases - of a phosphate group
C-Transaminases - of amino group
B-Transmethylases - of a methyl group
C-Transacetylases - of an acetyl group
4- Splitting or forming a C-C bond
A-Desmolases
5- Changing geometry or structure of a molecule
A-Isomerases
6- Joining two molecules through hydrolysis of pyrophosphate bond in ATP or other tri-phosphate
A- Ligases
Enzyme Kinetics: Energy Levels
The enzyme is thought to reduce the "path" of the reaction. This shortened path would
require less energy for each molecule of substrate converted to product.
Given a total amount of available energy, more molecules of substrate would be
converted when the enzyme is present (the shortened "path") than when it is absent.
Hence, the reaction is said to go faster in a given period of time.
Enzyme Kinetics: Basic Enzyme Reactions
The basic enzymatic reaction can be represented as follows
where E represents the enzyme catalyzing the reaction, S the substrate, the substance being
changed, and P the product of the reaction.
If this reaction is combined with the original reaction above equation the following results:
Chemical Equilibrium
The study of a large number of chemical reactions reveals that most do not go to true completion. This is
likewise true of enzymatically-catalyzed reactions. This is due to the reversibility of most reactions. In
general:
where K 1+is the forward reaction rate constant and K 1-is the rate constant for the reverse reaction.
Combining the two reactions gives:
Applying this general relationship to enzymatic reactions allows the equation:
Equilbrium, a steady state condition, is reached when the forward reaction rates equal the backward rates.
This is the basic equation upon which most enzyme activity studies are based.
Sugars Prefer To Be Cyclic
Carbohydrates Are Chiral
Molecules
Typically but not always
• L – amino acids
D
• D - sugars
Hence, these molecules
have a measurable optical
rotation, which depends
upon both the monomer
residues and their
conformation
L
Glyceraldehyde
Fisher Formulas
Next to last
carbon
determines
D or L
New carbon is added as C1
Hormones
A hormone
Is a chemical messenger that carries a signal
from one cell( or group of cells) to another via
the blood.
hormone : "A chemical secreted by cells in one part of
the body that is transported in the bloodstream to other
parts of the body, where it affects particular target
cells ".
-example: hypothalamus, pituitary
All multicellular organisms produce hormones
Endocrine hormone molecules are secreted
(released) directly into the bloodstream ,while
exocrine hormones (or ectohormones) are
secreted directly into a duct, and from the duct
they either flow into the bloodstream or they
flow from cell to cell by diffusion in a process
known as paracrine signalling.
Hierarchical nature of hormonal control
Hormonal regulation of some physiological activities involves a hierarchy of cell
types acting on each other either to stimulate or to modulate the release and
action of a particular hormone.
The secretion of hormones from successive levels of endocrine cells is stimulated
by chemical signals originating from cells higher up the hierarchical system.
The master coordinator of hormonal activity in mammals is the hypothalamus ,
which acts on input that it receives from the central nervous system
Other hormone secretion occurs in response to local conditions, such as the rate
of secretion of parathyroid hormone by the parathyroid cells in response to
fluctuations of ionized calcium levels in extracellular fluid.
Function of hormones
􀂄 HOMEOSTASIS
􀂄 Reproduction
􀂄 Growth and development
􀂄 Maintenance of internal environment
􀂄 Production, utilization and storage of
energy
Chemical nature of hormones
􀂄 Can be divided into 3 Groups:
􀂄 Amino acid derivatives
􀂄 Peptide hormones
􀂄 Lipid derivatives
Amino acid derivatives
􀂄 Derivatives of tyrosine
􀂄 Catecholamines (epinephrine,dopamine)
􀂄 Thyroid hormones (dipeptides)
􀂄 Tryptophan derivative
􀂄 Melatonin
Peptide hormones
􀂄 Glycoproteins from anterior pituitary
􀂄 thyroid-stimulating hormone (TSH)
􀂄 luteinizing hormone (LH)
􀂄 follicle-stimulating hormone (FSH)
􀂄 Peptides and small proteins
􀂄 Digestive tract hormones
􀂄 Pituitary hormones
􀂄 Pancreatic hormones
classes of lipid derived hormones
􀂄 Steroid hormones:
􀂄 derived from cholesterol
􀂄 2 groups
􀂄 with the intact steroid ring (adrenal and gonadal
steroids)
􀂄 with the steroid ring cleaved (metabolites of vit D)
􀂄 Eicosanoids:
􀂄 derived from arachidonic acid
Hormone receptors
􀂄 Molecules within or on the surface of target cells that bind hormones with high
affinity and specificity and thereby initiate and mediate biological responses
􀂄 Hormones will only produce the response in cells that express the receptors for
this particular hormone (target cells)
􀂄 ONLY target cells respond to hormone
􀂄 Cells that do not have receptors for the hormone “ignore” the hormone
Steroid hormones
The steroid hormones are all derived from cholesterol. Moreover, with the exception
of vitamin D ,they all contain the same cyclopentanophenanthrene ring and atomic
numbering system as cholesterol.
The important mammalian steroid hormones are shown below along with the structure
of the precursor, pregneolone. Retinoic acid and vitamin D are not derived from
pregnenolone, but from vitamin A and cholesterol respectively .
Vitamins
History
􀂄 Purified diets of carbohydrate, protein, fat,
minerals and water were not capable of
normal growth
􀂄 “Accessory growth factors”
􀂄 Casimir Funk, a Polish biochemist, isolated an
antiberberi substance from rice polishings
􀂄 Named it vitamine, an amine, vital for life
Vitamins
􀂄 Essential organic compounds required in very small amounts
(micronutrients)
involved in fundamental functions of the body
􀂄 Unrelated chemically
Vitamins
􀂄 Not metabolic fuels (like glucose or fatty acids) or structural nutrients
(like amino acids)
􀂄 Regulators (catalysts) of reactions, some of which are involved in
energy Metabolism
􀂄 Organic molecules in food
􀂄 Required in small amounts
􀂄 Classified based on solubility
􀂄 Fat soluble
􀂄 Water soluble
Classification of vitamins
Fat-soluble Vitamins
Water-soluble Vitamins
Vitamins
􀂄 All vitamins are metabolically essential but not all required in the diet
􀂄 Most mammals can synthesize vitamin C; not humans and primates
􀂄 No mammal can synthesize B vitamins but rumen bacteria do
The Basics of Water-Soluble Vitamins
􀂄 Dissolve in water
􀂄 B vitamins & vitamin C
􀂄 Absorbed mostly in small intestine & stomach
􀂄 Bioavailability
􀂄 Nutritional status, other nutrients & substances in food, medications,
age, illness
􀂄 Circulated to liver in blood
􀂄 Not stored in large quantities
The Basics of Water-Soluble Vitamins
Naming the Vitamins
􀂄 First named vitamin A or B
􀂄 B-complex vitamins
􀂄 Given common names also
􀂄 Thiamin
􀂄 Riboflavin
􀂄 Niacin
􀂄 Chemical names
􀂄 Ascorbic acid
Thiamin (Vitamin B1)
􀂄 Contains thiol & amine group (-SH) and (NH3)
􀂄 Thiamin pyrophosphate (TPP) or thiamin diphosphate
􀂄 Thiamin triphosphate
Functions of Thiamin
􀂄 ATP production
􀂄 Synthesis of DNA & RNA
􀂄 Noncoenzyme roles
Coenzyme Functions of Riboflavin (B2)
􀂄 Energy metabolism
􀂄 Redox reactions
􀂄 Formation of ATP, water, carbon dioxide
􀂄 β-oxidation
􀂄 Converts vitamin A & folate to active forms, tryptophan to niacin
􀂄 Forms vitamin B6 & K Riboflavin Deficiency
􀂄 Ariboflavinosis
􀂄 Weakness, cheilosis, stomatitis, glossitis, anemia, confusion
􀂄 Alcoholics
􀂄 Diseases that interfere w/ riboflavinutilization
Regulation of Vitamin B12 in the Body
􀂄 Must be cleaved before absorption
􀂄 Bound to R protein & intrinsic factor
􀂄 Once absorbed, binds to transcobalamin
􀂄 Circulates to liver via blood
􀂄 Stored in liver Functions of Vitamin B12 Coenzyme that catalyzes:
Production of succinyl CoA
􀂄 Uses amino acids & fatty acids for ATP production
􀂄 Conversion of homocysteine to methionine
􀂄 Allows use of folate
Regulation of Vitamin C in the Body
􀂄 Absorption in small intestine via active transport
􀂄 Uses glucose transport protein
􀂄 High intakes
􀂄 Absorbed by simple diffusion in stomach & small intestine
􀂄 Circulates to liver via blood
􀂄 Excess excreted in urine
Functions of Vitamin C
􀂄 Antioxidant
􀂄 Accepts & donates electrons
􀂄 Involved in a variety of redox reactions