LINKING OF ISOZYME AND CLASS VARIABILITY PATTERNS IN THE EMERGENCE OFNOVEL ALCOHOL-DEHYDROGENASE FUNCTIONS - CHARACTERIZATION OF ISOZYMES IN UROMASTIX HARDWICKII

The nature of the isozyme differences in the class-I alcohol dehydroge nase structure from the lizard, Uromastix hardwickii, was determined a nd related to those in the human and horse enzymes, for which isozyme structures have also been established. The Uromastix isozymes differ m uch (at a total of 72 positions, 19%) but, in spite of this, have simi lar properties and were not obtained resolved. Their structures were a nalyzed in mixture, and the two sub-sets of peptides obtained could be distinguished by evaluation of the recovery ratios within the peptide pairs. The isozymes have class-I activities, with an ethanol dehydrog enase activity of 0.6 U/mg and no formaldehyde dehydrogenase activity, have typical class-I structures, and are composed of N-terminally ace tylated 375-residue subunits (a and b). Importantly, variability patte rns between the isozymes are reminiscent of those both in the other tw o lines with isozymes (primates and horse) and in the class distinctio ns of the enzyme. Hence, the variability pattern since the distant sta ge of class-I emergence is also visible within the more recent isozyme divergence, illustrating a continuity in the evolution of isozymes to classes (and then to enzymes). The pattern also links the different l evels of multiplicity and may suggest an acceptability in common to du plications and mutations, compatible with the emergence of novel funct ions.