Enzyme polymorphism and adaptation

After a brief resume of the controversy concerning the adaptive value of enzyme polymorphisms, a physiological hypo thesis is advanced that heterosis for enzymes of intermediary metabolism results from the differential kinetic behavior of the alleles, which in heterozygotes serve to buffer rate-determining reactions from environmental perturbations. Polymorphism within a population of alpine butterflies is examined in some detail, and the results strongly implicate ongoing selective processes. A more detailed understanding would seem to require more pointed in vivo physiological analyses of the polymorphic variants. A characterization of the physical nature of the electrophoretic variants suggests that many variants do not involve a charge difference, while almost all involve a significant conformational difference. The value of explicit error estimates associated with each data characterization is stressed throughout.GEORGE B. JOHNSON, Department of Biology, Washington University, St. Louis, Missouri