Primary structures of dehydrogenases. Evolutionary characteristics related to functional aspects; models for isozyme developments and ancestral connections.

This chapter describes known characteristics of evolutionary changes in individual dehydrogenases, as well as possible relationships among this group of enzymes. Data from primary structures are correlated with those from other observations. Variations in the amino acid sequences demonstrate functional properties, and can be interpreted in relation to conformational aspects, subunit arrangements and enzyme stabilities. Different types of isozyme developments have occurred and show functional fixations at various levels. They define isozyme patterns of general significance in protein evolution. Sequence similarities may be found between different segments. They are analyzed in relation to known conformations, subunit sizes, species divergence and genetic mechanisms. A wide-ranging evolutionary model is discussed relating dehydrogenases and some other oligomeric enzymes to a distant, frequently remodelled ancestral building unit of repetitive occurrence.