Why are the structures related

Efficient catalysis requires a specific configuration of substrates and reactive residues, with groups (selected from a small number of suitable candidates) to serve as nucleophiles and electrophiles under physiological conditions. In enzymes catalysing similar reactions, some convergence towards similar spatial arrangements and functional groups at the active site must be expected. 

The gross structural characteristics of dehydrogenases therefore seem to derive from general properties of polypeptide chains, and it is found that similar tertiary structures have resulted from considerably different amino acid sequences. 

The steric course of reaction is determined by relatively non-specific interactions, such as van der Waal s contacts that would not allow a bulky group to be accommodated the other way round, and by specific interactions such as hydrogen bonds. 

It might at first seem wholly unimportant whether an aldehyde is reduced by Re or Si attack the same primary alcohol will result. However, if a related ketone serves as a poor substrate, the stereospecificity will determine whether the (R) or the (S) secondary alcohol is formed as an accompanying product. One or other may be advantageous to the organism for example, glycollate plus L-lactate as opposed to glycollate plus D-lactate. 

It is the spirit of the 1980s that all scientific endeavour should be useful. Finally, then, let it be recorded that the stereochemistry of dehydrogenases has important applications in biochemical analysis, in small-scale stereospecific syntheses, and in the design of therapeutic substances. 

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