ENZYMES

INTRODUCTION: In our daily life we have things that aid in smooth running of the others let’s say; in a motor engine you put oil to lubricate the engine.  In sauce, we put cooking oil to make it delicious.  On tea, we put sugar to make it sweet.  In the human body systems the enzymes act like sugar in tea, oil in an engine or cooking oil in sauce.   Enzymes are biocatalysts and protein in nature.  Life is possible due to the co-ordination of numerous metabolic reactions inside the cells.  Proteins can be hydrolyzed with hydrochloric acid by boiling for a very long time; but inside the body, with the help of enzymes, proteolysis takes place within a short time at body temperature.  Enzyme catalysis is very rapid; usually 1 molecule of an enzyme can act upon about 1000 molecules of the substrate per minute.  Lack of enzymes will lead to block in metabolic pathways causing inborn errors of metabolism.  The substance, upon which an enzyme acts, is called the substrate.  The enzyme will convert the substrate into the product or products.

CHARACTERISTICS OF ENZYMES:  Almost all enzymes are proteins.  Enzymes follow the physical and chemical reactions of proteins.  They are heat labile.  They are water-soluble.  They can be precipitated by protein precipitating reagents including ammonium sulfate or trichloroacetic acid.  They contain 16% weight as nitrogen.

CLASSIFICATION OF ENZYMES:  When early workers isolated certain enzymes, whimsical names were given.  Some of these, such as Pepsin, Trypsin, Chymotrypsin, and many others are still used.  Later, it was agreed to call the enzymes by adding the suffix "-ase" to the substrate.  Thus in that respect, enzyme Lactase acts on the substrate lactose, and the products glucose and galactose are formed.  Enzymes that hydrolyse starch (amylose) are termed as amylases; those that dehydrogenate the substrates are called dehydrogenases.  These are known as the trivial names of the enzymes.  

OXIDOREDUCTASES:  Transfer of hydrogen or addition of oxygen; e.g. Lactate dehydrogenase (NAD); Glucose-6-phosphate dehydrogenase (NADP); Succinate dehydrogenase (FAD); di-oxygenases.  

TRANSFERASES: Transfer of groups other than hydrogen.  Example, Aminotransferase. (Subclass: Kinase, transfer of phosphoryl group from ATP; e.g. Hexokinase).  

HYDROLASES: Cleave bond and add water; e.g. Acetyl choline esterase; Trypsin.  

LYASES: Cleave without adding water, e.g. Aldolase; HMG CoA lyase; ATP Citrate lyase. (Subclass: Hydratase;add water to a double bond).  

ISOMERASES: Intramolecular transfers. They include racemases and epimerases. Example, Triose phosphate isomerase.  

LIGASES: ATP dependent condensation of two molecules, e.g. Acetyl CoA carboxylase; Glutamine synthetase; PRPP synthetase.

RELATED;

1.  INSULIN  

2.  GLUCAGON

3.  BIOCHEMISTRY
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