Structure and expression of mammalian carbonic anhydrases.

tions make it possible to ascribe specific roles to particular residues, such as the conserved glycine residues 141 at bends in the basic fold which appear to constitute alcohol dchydrogenase per se. Each of these concepts can now be further tested by directed mutagenesis. Regarding the enzymic mechanisms, the basic properties of the zinc dehydrogenases have essentially been known for some time. However, the short-chain dehydrogenase type is largely unknown in mechanistic terms and studics of additional forms, complemented with extensive comparisons, should be valuable also for the short-chain dehydrogenase group, to define more constant segments and particularly conserved residues which can then be directly tested for in mechanistic and functional terms. For example, a segment around position 150 in the short-chain dehydrogenases appears likely to be close to the active site and has a few conserved residues of particular interest 161. I t is t o be expected that further studies of natural variants will increase the reliability in the interpretational conclusions.