Dehydrogenases mononucleotide binding unit

The differences in quaternary structure as opposed to the preservation of tertiary structure of the NAD+ binding domains suggest that subunit associations are of more recent origin (9). Buehner et al. 17) used the preservation of the Q axis in GAPDH, LDH, and s-MDH, and the close resemblance of the dimer of s-MDH to one-half of the LDH molecule, to suggest an evolutionary tree (Fig. 12). Also included in Fig. 12 is the relationship of an FMN mononucleotide binding unit in flavodoxin 24) to the dehydrogenases. 

In this chapter, the word domain is defined as the complete NAD+ binding segment in any one dehydrogenase. Thus this usage differs to that of Rossmann and Liljas (W) where a domain specifies a mononucleotide binding structure only. The latter will be called a mononucleotide unit here. 

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