The structure of enzymes; summery

The two substrates S1 and S2 connect very specifically to the enzym. Other molecules don't fit there (in a way of shapes)
Regularly but not in all cases, in the action centre of the is a co-(weakly bonded) or a prostetic group (strong bonded)
Changes in the shape of the action centre can strongly influence the enzyme activity, even stop it.
The centre often is situated in a kind of non polar clove.

Co-enzymes and prostetic groups ( ) improve the enzyme activity.

The complete enzym, including the cofactors and prostetic groups, are called the holo-enzym,
The enzyme without cofactors and prostetic groups are called the apo-enzym.

Regularly the co-enzyme is a vitamine, and the same co-enzyme can serve different enzyms.
Some enzyms need an inorganic part like a metal ion (examples: Ca2+, Mg2+ of Zn2+).
These inorganic component is an 'activator'. In a functional way the activator equals a co-enzym, but the inorganisc components are not called: co-enzymes.

The enzyme is - in a structural view - just a normal protein with: