Characterization of mutation-induced changes in the maize (Zea mays L.) ADH1-1S1108 alcohol dehydrogenase

The homodimeric alcohol dehydrogenase gene produce of maize (Zea mays L.) Adh1-1S1108 mutation was purified and compared with the parental Adh1-1S enzyme. The mutant alcohol dehydrogenase activity had pH optima and substrate specificity similar to those of the parental enzyme, but exhibited somewhat increased and decreased Km values for acetaldehyde and NADH, respectively. The mutant enzyme was also markedly less stable than the enzyme from parental tissues to temperatures as low as 50 degrees C. Sequence analysis of a polymerase chain reaction (PCR)-generated cDNA clone revealed a G-to-C mutation at position 406 and a C-to-T mutation at position 974. These would result in residue 103 of each protein subunit being changed from an alanine to a proline and residue 292 being changed from an alanine to a valine. Whether one or both of these changes in primary sequence is responsible for the altered substrate affinities and stability is not yet understood.