LESSON 6 Nomenclature and definition of enzymes

 

   Enzymes are complex globular protein catalysts that accelerate chemical reaction rates by factors of 1012-1020 over that of uncatalyzed reactions at temperatures around 37℃.By contrast, industrial catalysts (inorganic substances) are orders of magnitude less effective than enzymes under comparable conditions. For example the reduction of hydrogen peroxide catalyzed by cataloes ,occurs 10 million times faster than it does when catalyzed by colloidal platinum at 37℃.

The catalytic efficiency of enzymes is very high, whereby one molecule of enzymes can transform as many as 10,000-1,000,0000 molecules of molecule of substrate per minute. it is this catalytic efficient of enzymes at low temperature which makes them important to the food scientism. This means that foods can be processed or modified by enzymes at moderate temperature ,say 25-50℃,where food products would not otherwise undergo changes at a significant rate .It also means, however, that endogenous enzymes are active under these conditions as well, and this can be beneficial or deleterious

Furthermore, enzymes because of their tremendous catalytic power and low activation energies are active at subfreezing temperatures and therefore can be important stimulants of degradative reactions in refrigerated or frozen foods.

Of course, one basis for heat processing is to denature and inactivate enzymes so that the food is not subjected to continuing enzymes activity. The food scientist must have an understanding of the denaturtion phenomenon in order to properly process foods.

Another important aspect of enzymes activity in addition to catalytic power is the specificity of enzymes reactions. Industrial catalysts lack this specificity of reaction, and so cannot be used for modifying specific components of a food system. The specificity of hydrogen ion catalysts, for example, is very broad, whereas many enzymes perform only a single function, such as hydrolysis of a single bond or bond type. It is this enzymes specificity, which allows the food scientist to selectively modify individual food components and no affect others.

The sensitivity and specificity of enzymes also make them important to the food scientist as analytic tools. Analysis for food constituents in many instances can be simplified using enzymes techniques, which are detailed by berg Meyer, and jailbait.

 

Enzymes nomenclature

 

Over the years, the number of enzymes isolated and characterized has continued to increase at an enormous rate. Previously it was custom for individual who isolated and characterized the enzyme to also name it. However, in many instances the same name. Consequently, the nomenclature for enzymes because so chaotic that the international union of biochemistry instituted a commission on nomenclature and classification of enzymes to prepare a system of nomenclature that has become standard and should be used in enzyme work. Each enzyme is assigned a code number of four numerals, each separated by periods and arranged according to the following principles .

The first numeral is the main division to which the enzyme belongs, i.e. (1) oxidoreductases, (2) transferases, (3) hydrolase, (4) lyases, (5) isomerases, and (6) ligases; the second is the subclass which identifies the enzyme in more specific terms; the third precisely defines the type of enzyme activity; and the fourth numerals clearly number of the enzyme in its sub-subclass.

Thus the first three numerals clearly designate the nature of the enzyme. For example, 1.2.3.4 denotes an oxidoreductase with an aldehyde as a donor and O2 as an acceptor, and it is the fourth numbered enzyme in particular series. In addition to the code number each enzyme is assigned a systematic name, which in many instances is too cumbersome to be used in the literature on a routine basis. Consequently, a trivial name has been recommended of common usage. The trivial name is sufficiently short for general use but is not necessarily very exact or systematic; in a great of the international union of biochemistry o nomenclature and classification of enzymes catalogued over 1700 enzymes each.

Aside from enzymes involved in postmortem and post harvest physiogy, few of the catalogued enzymes are of direct interest to the food scientist. By far the largest group of enzymes used in food processing is the hydrolases. A few oxidoreductases and isomerases are used, but hardly any transferees, assessor lipases.

 

Definitions

 

The following terms are encountered in the enzymology literature.

 

  1. Holoenzyme: The protein portion of the enzyme and the coenzyme, it needed for catalytic activity.     

  2. Apoenzyme: The thermolabile protein component of the enzyme theat determines specificity.

3. Coenzyme, cofactor, prosthetic group: These terms are often used interchangeably to describe cocatalsts which act in conjunction with the apoenzyme to catallyze a reaction. However, Bernhard draws a distinction between cofactors and coenzymes. Prosthetic groups are usually those cocatalysts that are very tightly bound to the protein.

  4. Isoenzymes or isozymes: Multiple forms of an enzyme occurring in the same species. They catalyze the same reaction and arise from genetically determined differences in primary structure.The term "multiple forms of the enzyme " should be used as a broad term covering all proteins possessing the same enzymic activity and occurring naturally in a single species.