Enzymes should be characterized by flexibility and presence of numerous functional groups. Proteins are the only organic molecules, which fit these requirements. They are formed by 20 different subunits, which have different functional groups possibly used in catalysis. At the same time, protein chain is flexible and can bend to form a number of different structures with respect to amino acid sequence. Moreover, proteins are large molecules, which ensures their stability, and it is important for efficient catalysis.
I so far am very satisfied. I think the only complaints I would have are today the work was a little late, and the pricing seems inconsistent, but the representatives are very helpful in alleviating those problems.