Principles of Biochemistry

Enzymes are soluble, colloidal catalysts formed by living cells, specific in action and protein in nature. They have molecular weights ranging from about 12,000 to over 1 million. They are therefore very large compared with the substrates or functional groups they act up on.

They are inactive at 0^oC and destroyed by moist heat at 100^oC. Enzymes have extraordinary catalytic power, which is generally far greater than that of synthetic catalysts. They have a high degree of specificity for they are biocatalysts which they accelerate specific chemical reactions without formation of by-products, and they function in dilute aqueous solutions under very mild conditions of temperature and pH.

Types of enzyme

Some enzymes consist only of polypeptides and contain no chemical groups other than amino acid residues; E. g. pancreatic ribonuclease.

Other enzymes, however, require for activity an additional chemical component called a cofactor or an organic molecule called coenzyme.  

The protein part of an enzyme is called as apoenzyme. •A complete, catalytically active enzyme together with its coenzyme or metal is called holoenzyme.