The use of enzymes - employed either as isolated enzymes, crude protein
extracts or whole cells - for the transformation of non-natural organic
c- pounds is not an invention of the twentieth century: they have been
used for more than one hundred years. However, the object of most of the
early research was totally different from that of the present day.
Whereas the elucidation of biochemical pathways and enzyme mechanisms
was the main driving force for the early studies, in contrast it was
mainly during the 1980s that the enormous potential of applying natural
catalysts to transform non-natural organic c- pounds was recognized.
This trend was particularly well enhanced by the recommendation of the
FDA-guidelines (1992) with respect to the use of chiral bioactive agents
in enantiopure form. During the last two decades, it has been shown that
the substrate tolerance of numerous biocatalysts is often much wider
than previously believed. Of course, there are many enzymes which are
very strictly bound to their natural substrate(s). They play an
important role in metabolism and they are gener- ly not applicable for
biotransformations. On the other hand, an impressive number of
biocatalysts have been shown to possess a wide substrate tolerance by
keeping their exquisite catalytic properties with respect to chemo-,
reg- and, most important, enantio-selectivity. This made them into the
key tools for biotransformations.