Role of Enzymes in Nutrition
Enzymes are chemical substances produced in the
living organism. They are marvellous organic catalysts which are essential to
life as they control all the chemical reactions that take place in a living
system. Enzymes are part of all living cells, including those of plants and
animals. The term enzyme, which literally means in yeast’, was coined following
the demonstration of catalytic properties of yeast and yeast juices. Although
enzymes are produced in the living cell, they are not dependent upon the vital
processes of the cell and work outside the cell. Certain enzymes of yeast, for
instance, when expressed from the yeast cells are capable of exerting their
usual effect, that is, the conversion of sugar to alcohol. A striking feature
of enzymes is that while they enter into chemical reaction, they remain intact
in the process. They however, act with maximum efficiency at a certain
temperature. Lowering the temperature below or raising it above this level
slows the reaction. A high degree of heat, that is above 60°C, permanently
destroys their action. It has been estimated that there are over 20,000 enzymes
in the human body. This estimate is based on the number of bodily processes
that seem to require action. However, so far only about 1,000 enzymes have been
identified. But their great role in nutrition and other living processes has
been firmly established. They are protein molecules made up of chains of amino acids.
They play a vital role and work more efficiently than any reagent concocted by
chemists. Thus for instance, a chemist can separate proteins into their
component amino acids by boiling them at 166°C for over 18 hours in a strong
solution of hydrochloric acid, but the enzymes of the small intestines can do
so in less than three hours at body temperature in a neutral medium. A feature
which distinguishes enzymes from inorganic catalysts is that they are
absolutely specific in their actions. This means that a particular enzyme can
cause reactions involving only a particular type of substance or a group of
closely related substances. The substance on which the enzyme acts is known as
"substrate". The specificity of an enzyme is, however, related to the
formation of the enzyme-substrate complex which requires that the appropriate
groupings of both substrate and enzyme should be in correct relative position.
The substrate must fit the enzyme like a key fits its lock. Enzymes which are
used in the cells which make them are called intracellular enzymes. Enzymes
which are produced in cells which secrete them to other parts of the body are
known as extracellular enzymes. Digestive juices are an example of the latter
type.
Nomenclature
There are few enzymes whose names have been
established by long usage such as ptyalin, pepsin, trypsin and erepsin. Apart
from these, enzymes are usually named by adding the suffixes to the main part
of the name of the substrate upon which they act. Thus amylases act upon starch
(amylum), lactase acts upon lactose, lipases act upon lipids, maltase acts upon
maltose and protesses act upon lipids, maltase acts upon maltose and protesses
act upon proteins. There are, however, several enzymes which act upon many
substances in different ways. These enzymes are named by their functions rather
than substrates. Thus, an enzyme which causes deaminations is called a
deaminase and oxidising enzyme an oxidase. Some enzymes work efficiently only
if some other specific substance is present in addition to substrate. This
other substance is known as an "activator" or a "coenzyme".
"Activators" are usually inorganic ions. They increase the activity
of a complete enzyme and may take part in the formation of the enzyme-substrate
complex. Many of the coenzymes are related to vitamins. This explains why
vitamin deficiencies profoundly alter metabolism. Thus, for instance, thiamine,
as thiamine pyrophosphate, functions as a coenzyme in at least 14 enzymes
systems. Coenzymes, like enzymes, are being continuously regenerated in the
cells.
Enzymes play a decisive role in the digestion of food as they are
responsible for the chemical changes which the food undergoes during digestion.
The chemical changes comprise the breaking up of the large molecules of
carbohydrates, fats and proteins into smaller ones or conversion of complex
substances into simple ones which can be absorbed by the intestines. They also
control the numerous reactions by which these simple substances are utilized in
the body for building up new tissues and producing energy. The enzymes
themselves are not broken down or changed in the process. They remain as
powerful at the end of a reaction as they were at the beginning. Moreover, very
small amounts can convert large amounts of material. They are thus true
catalysts. The process of digestion begins in the mouth. The saliva in the
moth, besides helping to masticate the food, carries an enzyme called ptyalin
which begins the chemical action of digestion. It initiates the catabolism
(breakdown) of carbohydrates by converting starches into simple sugars. This
explains the need for thorough mastication of starchy food in the mouth. If this
is not done the ptyalin cannot carry out its functions as it is active in an
alkaline, neutral or slightly acid medium and is inactivated by the highly acid
gastric juices in the stomach.
Although enzymatic action starts while food is
being chewed, digestion moves into high gear only when the chewed food has
passed the esophagus and reached the stomach. While the physical action of
peristalsis churns and kneads solid food into a semi-solid amorphous mixture called
chyme, this mixture undergoes chemical changes initiated by gastric juices
secreted by the walls of the stomach. These juices include mucus for
lubricating the stomach, hydrochloric acid and gastric juice. The enzyme or
active principle of the gastric juice is pepsin. This enzyme in combination
with hydrochloric acid starts the breakdown of proteins into absorbable aminoacids
called polypeptides. An additional enzyme, rennin, plays an important role in
the stomach of the infant. It curdles milk and allows the pepsin to work upon it.
The gastric juice has no effect upon starches or fats. When the chyme leaves
the stomach and enters the small intestine through the pylorus – the lower
escape valve, it still contains much food which is in the form of raw material
not yet ready for absorption in the body. Digestion is completed inside the
small intestine by several juices. From liver comes a liquid called bile which
converts fat globules into a smooth emulsion. The pancreas contributes various
enzymes which continue the breakdown of proteins, help to divide starch into
sugars and work with bile in digesting fats. The small intestine itself
secretes enzymes from its inner wall to complete the reactions. When all the
enzymes have done their work, the food is digested and rendered fit for absorption
by the system.
Enzymes form part of the food we eat. Raw foods
contain enzymes in abundance; cooking, pasteurising, pickling, smoking and
other processings denature enzymes. It is, therefore, essential to include in
our diet, substantial amount of raw foods in the form of fruits, raw salads and
sprouts. Studies have revealed that the body without sufficient raw materials
from raw foods, may tire and produce fewer enzymes year after year. This may
lead to wearing out of
body processes and
consequent worn-out looks.
Source: www.healthlibrary.com through
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