METABOLIC EVOLUTION IN ALPHA-AMYLASES HORN DROSOPHILA-VIRILIS AND DROSOPHILA-REPLETA, 2 SPECIES WITH DIFFERENT ECOLOGICAL NICHES

alpha-Amylases from Drosophila virilis and D. repleta were partially p urified by ion exchange chromatography. The two amylases share common characteristics for pH and cations effects, although with slight diffe rences. D. virilis has optimal activity at pH 6.6 and D. repleta at pH 7.2. Calcium, sodium, and potassium cations activate amylolytic activ ity in both species but Ba2+ has an activation effect in D. repleta on ly. In contrast, there are major differences in thermal stability and kinetics among amylases of the two species. D. virilis amylase is much more stable at high temperature and the optimal temperatures are very different between the two species, respectively, 45 degrees C and 30 degrees C for D. virilis and D. repleta. alpha-Amylase activity using different substrates is greater on starch than on glycogen in both spe cies and still higher on amylose for D. virilis, the nonfungus feeder species. alpha-Amylase of D. repleta, the mycophagous species, has a b etter affinity to amylopectin and glycogen. Such differences in substr ate specificity suggest adaptation to different resources in these spe cies living in different habitats. Metabolic evolution seems to have o ccurred through a ''tradeoff'' between kinetic effectiveness and the n ature of substrate, with a higher V-max on amylose for D. virilis and a lower K-m on glycogen for D. repleta. (C) 1998 Elsevier Science Inc.