Effects of homozygosity and heterozygosity on certain properties of genetically defined electrophoretic variants of alcohol dehydrogenase isozymes in maize

Summary

Genetically defined alcohol dehydrogenase isozymes have been studied. The faster electrophoretically migrating forms of both Adh-1 and Adh-2 have greater specific activity and are more heat stable than the alternative slow forms of the two isozymes. In the heterozygous state, it is confirmed by genetic dosage studies that the Adh-2 F/F homodimer is more catalytically active than the S/S homodimer. The heat stability relationship between the two homodimers is maintained in the heterozygous condition. Adh-1 also has the same heat stability when taken from the heterozygous as well as the homozygous background. The heterodimeric, hybrid molecules (F/S and S/F for Adh-2) have less catalytic activity than the F/F homodimer but more than the homodimer S/S enzyme. This is concluded from studies in the triploid endosperm where the effects of genetic dosing can be investigated. The hybrid enzymes have heat stability similar to the F/F homodimer. The finding that allelic forms of an enzyme can show altered properties of possible physiological advantage to the organism is discussed in relation to fitness of the alternative forms.