Re: What does enzyme mean?

Enzymes are the large group of proteins, which can be defined as 
biocatalysators of various metabolic reactions. In simple words an enzyme 
"speeds up" the reaction process. Thus, the reactions which normally would 
require several hours, weeks, or months can be completed within 
miliseconds. The enzyme is involved in lowering the energy level required 
for the reaction to be run. There are specific enzymes for each reaction 
occuring in metabolism of a living organism. We define six major groups of 
the enzymes depending on the specificity of the reaction catalysed by them:

- Oxidoreductases - participating in red-ox reactions
- Transferases - participating in tranferring certain groups from one 
molecule to another
- Hydrolases - participating in hydrolytic cleavage of the bond in the 
molecule
- Lyases - participating in splitting the molecule into smaller products
- Isomerases - participating in changing the molecule into its isomeric 
form
- Ligases - participating in merging two or more molecules into one.

The enzymes are proteins. Often they have a non-protein components (heme, 
nucleotide derivatives, vitamins, carbohydrates, lipids etc.) which are 
necessary for their action. These components often form so-called catalytic 
site directly involved in the reaction catalysis. The catalytic site can be 
formed also by the fragments of the enzymatic protein itself, or by just 
several amino acid residues which are constituents of this protein. The 
other important site in enzyme is substrate site (or substrate pocket) 
which is responsible for the recognition of the substrate - the molecule to 
be processed during the reaction. 
The enzyme action can be regulated (accelerated or inhibited) by other 
compounds. For this reason there are sites specifically responsible for 
binding such modulators. The complex enzyme-modulator sligthly changes the 
conformation (shape) of the enzyme molecule - that implies changes in 
catalytic enzyme properties also.
We can say, that almost all metabolic reactions in our organism are 
enzymatically "supported".