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 allozy me could be due to its biochemical impairment relative to the common a llozyme, biochemical properties such as catalytic efficiency and confo rmational stability of the rare (ARK(B)) and the common (ARK(A)) alloz ymes were compared in this study. Both allozymes were purified by ammo nium 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 Vmax or Vmax/Km than ARK(B) at 18 or 29 degrees C, but there are no differences at 24 degrees C. I n general, ARK(A) is catalytically more efficient than ARK(B). Heat tr eatment of the allozymes shows that ARK(B) has a lower specific activi ty 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 partia lly account for the rarity of Argk(B) in natural populations of D. mel anogaster.