The relative quantities and catalytic activities of enzymes produced by alleles at the alcohol dehydrogenase locus in Drosophila melanogaster

Abstract

We have examined the kinetic properties of enzymes produced by the electrophoretically fast (F) and slow (S) alleles at the alcohol dehydrogenase locus in a polymorphic laboratory population of Drosophila melanogaster. The product of the F allele has approximately twice the specific activity of the product of the S allele. We have estimated four Michaelis constants (K _ethanol, K _NAD, K′_ethanol, and K′_NAD) and have found no significant difference between the major (ADH-5) isozyme produced by homozygotes for the two alleles. The relative amounts of enzyme produced by the homozygotes were estimated by the method of Laurell (1966), and again no significant differences were found. It appears that the difference in specific activities can be explained solely in terms of relative catalytic efficiency. In a series of laboratory stocks, those fixed for the F allele tend to produce more enzyme than those fixed for the S allele. These observations do not support the view that the alleles are selectively equivalent.