Properties of Enzymes

Lesson 12 : Enzymes-Nature, Classifications and Functions

Properties of Enzymes

Characteristics of enzymes

  1. biological catalysts
  2. not consumed during a chemical reaction
  3. speed up reactions from 1000 - 1017, with a mean increase in rate of 00,000
  4. exhibit stereospecificity --> act on a single stereoisomer of a substrate
  5. exhibit reaction specificity --> no waste or side reactions

All known enzymes are proteins. They are high molecular weight compounds made up principally of chains of amino acids linked together by peptide bonds.

Enzymes can be denatured and precipitated with salts, solvents and other reagents. They have molecular weights ranging from 10,000 to 2,000,000.

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.

Apoenzyme + Cofactor = Holoenzyme

According to Holum, the cofactor may be:

  1. A coenzyme - a non-protein organic substance which is dialyzable, thermostable and loosely attached to the protein part.
  2. A prosthetic group - an organic substance which is dialyzable and thermostable which is firmly attached to the protein or apoenzyme portion.
  3. A metal-ion-activator - these include K+, Fe++, Fe+++, Cu++, Co++, Zn++, Mn++, Mg++, Ca++, and Mo+++.

Specificity of Enzymes

One of the properties of enzymes that makes them so important as diagnostic and research tools is the specificity they exhibit relative to the reactions they catalyze. A few enzymes exhibit absolute specificity; that is, they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. In general, there are four distinct types of specificity:

  1. Absolute specificity - the enzyme will catalyze only one reaction.
  2. Group specificity - the enzyme will act only on molecules that have specific functional groups, such as amino, phosphate and methyl groups.
  3. Linkage specificity - the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure.
  4. Stereochemical specificity - the enzyme will act on a particular steric or optical isomer.

Though enzymes exhibit great degrees of specificity, cofactors may serve many apoenzymes. For example, nicotinamide adenine dinucleotide (NAD) is a coenzyme for a great number of dehydrogenase reactions in which it acts as a hydrogen acceptor. Among them are the alcohol dehydrogenase, malate dehydrogenase and lactate dehydrogenase reactions.

Last modified: Thursday, 19 January 2012, 9:18 AM