CHAPTER ONE
INTRODUCTION AND LITERATURE REVIEW
1.1 Enzyme
Enzymes are large biological molecules
responsible for thousands of chemical inter-conversions that sustain
life (Smith, 1997). All known enzymes are proteins. They are high
molecular weight compounds made up principally of chains of amino acids
linked together by peptide bonds, they are denatured at high temperature
and precipitated with salts, solvents and other reagents. They have
molecular weights ranging from 10,000 to 2,000,000 units. Enzymes do not
cause reactions to take place, but rather they enhance the rate of
reactions that would have been slower without their presence and still remains unused and unchanged.
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-ionactivator) is called the holoenzyme (Alexopoulos et al., 1996)
The living cell is the site of
tremendous biochemical activity called metabolism. It is the process of
chemical and physical change which goes on continually in the living
organism involving the build-up of new tissues, replacement of old
tissue, conversion of food to energy, disposal of waste materials,
reproduction - all the activities that we characterize as
"life."Thephenomenon of enzyme catalysis makes possible biochemical
reactions necessary for all life processes. Catalysis is defined as the
acceleration of a chemical reaction by some substance which itself
undergoes no permanent chemical change. Synthetic molecules called
artificial enzymes also display enzyme like catalysis (Grovesm, 1997).
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(Bairoch,
2000).
Enzymes actually work by lowering the
activation energy of a reaction. This is achieved when it creates an
alternative pathway which is faster for the reaction hence speeding it
up such that products are formed faster. Enzyme catalysed reactions are
million times faster than uncatalysed reactions, they alter the rates
but not the equilibrium constant of the reaction being catalysed
(Ashokkumar et al., 2001). A few RNA molecules called ribozymes
also catalyse reactions, with an important example being some parts of
ribosome (Lilley, 2005).
1.1.1 Types of enzymes
Metabolic enzymes:
These have been called the spark of life, the energy of life and the
vitality of life. These descriptions are not without merit. Metabolic
enzymes catalyse and regulate every biochemical reaction that occurs
within the human body, making them essential to cellular function and
health (Sangeethaet al.,2005). Digestive enzymes turn the food
we eat into energy and unlock this energy for use in the body. Our
bodies naturally produce both digestive and metabolic enzymes as they
are needed. They either speed up or slow down the chemical reactions
within the cells for detoxification and energy production. The enable us
to see, hear, and move and think. Every organ, every tissue and all 100
trillion cells in our body depend upon the reaction of metabolicenzymes
and enjoy their energy factor. Without these metabolic enzymes,
cellular life would beimpossible.
Food enzymes:These are
introduced to the body through the raw foods we eat and
throughconsumption of supplemental enzyme products. Raw foods naturally
contain enzymes providing asource of digestive enzymes when
ingested(Hossainet al., 1984). However, raw food manifests only
enough enzymesto digest that particular food, not enough to be stored
in the body for later use (the exceptionsbeing pineapple and papaya, the
sources of the enzymes bromelain and papain). The cooking andprocessing
of food destroys all of its enzymes. Since most of the foods we eat are
cooked orprocessed in some way and since the raw foods we do eat
contain only enough enzymes toprocess that particular food (Persike et al.,
2002) our bodies must produce the majority of the digestive enzymes
werequire, unless we use supplemental enzymes to aid in the digestive
process. A variety ofsupplemental enzymes are available through
different sources. It is important to understand thedifferences between
the enzyme types and ensure that one is using an enzyme product which
willmeet one’s particular needs.
Plant based enzymes:These are the most popular choice of enzymes. They are grown in a laboratorysetting and extracted from Aspergillus species. The enzymes harvested from Aspergillusspecies
are called plantbased, microbial and fungal. Of all the choices, plant
based enzymes are the most active. Thismeans they can break down more
fat, protein and carbohydrates in the broadest pH range than any other
sources (Ashokkumar et al., 2001).
1.1.2 Characteristics of enzymes
Protein nature:Enzyme is a protein. The main components of an enzyme is protein.
Temperature:Enzymes are
sensitive to temperature. Many work best at temperatures close to body
temperatures and most lose their ability to catalyse if they are heated
above 60 or 70o C. (Ashokkumar et al., 2001).
Acidity and alkalinity:Many enzymes work best at a particular pH and stop working if the pH becomes too acidic or alkaline.
Catalytic effect:It
acts as catalyst, enzyme functions in accelerating chemical reaction,
but the enzyme itself does not change after the reaction ends.
Specificity:It
functions specifically. The enzyme only catalyzes one kind of substrate
and cannot function for many substrates. The term is called one enzyme
one substrate.
Reversibility: It means
the enzyme does not determine the direction of reaction, but it only
functions in accelerating reaction rate until it reaches equilibrium.
The enzyme also functions in substance synthesis and substance breaking
down reaction.
Small quantity:It is required, in small amount. A small amount of enzyme is able to catalyze a chemical reaction (Nason, 1968).