Biochemical Comparison of Arginine Kinase Allozymes in Drosophila melanogaster

ARK^B 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 (ARK^B) and the common (ARK^A) 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. ARK^A has a higher Vmaxor Vmax/Km than ARK^B at 18 or 29°C, but there are no differences at 24°C. In general, ARK^A is catalytically more efficient than ARK^B. Heat treatment of the allozymes shows that ARK^B has a lower specific activity than ARK^A, and its temperature of heat inactivation is also lower. Also, the rate of heat inactivation of ARK^B is faster. Therefore, ARK^B is more thermolabile than ARK^A. From comparisons of catalytic efficiency and thermal stability of the allozymes, we assume that ARK^B is biochemically less efficient than ARK^A, and that might partially account for the rarity of Argk^B in natural populations of D. melanogaster.