Unit-1: Enzymology and Metabolism
Introduction:
Enzymes are biocatalysts—Catalysts of life
A catalyst is defined as a substance that increases the velocity or the rate of a chemical reaction, without itself undergoing any change in the process
Enzymes are biocatalysts that are synthesized by living cells.
They are proteinaceous (exception is the ribozyme, which is an RNA), colloidal, and thermolabile (inactive at 0C and destroyed at 100C)
They are specific in action, catalyze all biochemical reactions and are susceptible to many factors like temperature, pH, etc.
Examples: urease, carbonic anhydrase, pepsin, rennin, etc. the word enzyme was used by Kuhne 1878, to indicate the catalysis taking place in the
biological systems. lsolation of enzyme system from cell-free extract of yeast was achieved in 1883 by Buchner. He named the active principle as zymase (later found to contain a mixture of enzymes), which could convert sugar to alcohol. Sumner first achieved the
isolation and crystallization of the enzyme urease from jack bean and identified it as a protein.
1. Chemical Nature and Properties of Enzymes
Each enzyme has its own tertiary structure and specific conformation, which is very essential for its catalytic activity
Chemically, enzymes may be divided into 2 categoriesSimple protein enzymes
These contain simple proteins only. E.g., urease, amylase, papain, etc.
Complex protein enzymes
These contain conjugated proteins, i.e., they have a protein part called apoenzyme and a non-protein part called prosthetic group, associated with the protein unit
The 2 parts together constitute the holoenzyme. E.g., catalase, cytochrome c, etc.
Holoenzyme
o The functional unit or the active structure of an enzyme (apoenzyme + prosthetic
group) is called holoenzyme
Holoenzyme Apoenzyme Coenzyme
(Active enzyme) (Protein part) (Prostetic group)
