Biotransformations with Saccharomyces cerevisiae (baker´s
yeast) play an important role in modern stereoselective chemical synthesis.
With the help of this microorganism reactions are catalysed which classical-chemically
can be realised only worse or even not at all.
On the other hand, with living microorganisms the selective conversion of a substrate by a single enzyme to a single product is the ideal case.
Living cells are highly complex systems, and microbial syntheses therefore depend on culture and reaction conditions. These exert a great effect on cell physiology and thus on the outcome of the overall reaction. For these reasons, the elucidation of the processes involved in a whole-cell biotransformation bears a great potential for the development of highly selective biocatalytic reactions. Also with regard to biotransformations, S. cerevisiae is one of the best explored microorganisms.
It is a fact that whole-cell biotransformations may suffer from the opposite-directed stereoselectivities of enzymes which act simultaneously on the same substrate. Latest approaches to inhibit undesired stereoselectivity have been very successful - with the drawback that these methods, although highly effective, are the result of intensive empirical studies.
Further, every biocatalytic method requires very special conditions. The determination of the best process parameters is demanding.
It is therefore necessary to gain a concise understanding of the enzymatic network. For the investigation of stereoselective reductions, time-dependent changes in intracellular NADH concentration are a promising tool for getting deeper insight into how enzymes interact during a biotransformation.
Finally, mathematical methods are expected to provide substantial help
in understanding and controlling biotransformations with living cells.
References:
M. Bertau, Biospektrum 2002, 8, in press.
M. Bertau, Tetrahedron Lett. 2001, 42, 1267-1268.
M. Bertau, M. Bürli, Chimia 2000, 54, 503-507.