ARKB is a rare arginine kinase allozyme found in natural populations of Drosophila melanogaster. To test whether the rarity of this allozyme could be due to its biochemical impairment relative to the common allozyme, biochemical properties such as catalytic efficiency and conformational stability of the rare (ARKB) and the common (ARKA) allozymes were compared in this study. Both allozymes were purified by ammonium sulfate fractionation, DEAE-ion-exchange column, Blue-Sepharose, and S-300 gel filtration, to yield a single coomassie-blue band on SDS-polyacrylamide gels. ARKA has a higher Vmax or Vmax/Km than ARKB at 18 or 29°C, but there are no differences at 24°C. In general, ARKA is catalytically more efficient than ARKB. Heat treatment of the allozymes shows that ARKB has a lower specific activity than ARKA, and its temperature of heat inactivation is also lower. Also, the rate of heat inactivation of ARKB is faster. Therefore, ARKB is more thermolabile than ARKA From comparisons of catalytic efficiency and thermal stability of the allozymes, we assume that ARKB is biochemically less efficient than ARKA, and that might partially account for the rarity of ArgkB (3 in natural populations of D. melanogaster.
Drosophila melanogaster, Arginine kinase allozymes, Catalytic efficiency, Conformational stability
