Thermolabile variant, PHOX-S, of prophenol oxidase in Drosophila melanogaster

The Phox(S) strain of Drosophila melanogaster is an electrophoretically slow variant found in a wild population at Victoria, Australia. Prophenol oxidase isoform A(1) from PHOX-S was purified and characterized biochemically and genetically. The purified fraction of A(1) from PHOX-S showed a homodimer with a molecular weight of the subunit of approximately 77 kDa. The Phox(S) strain was temperature sensitive in vivo in culture, and the purified protein was thermolabile in vitro. By the deletion mapping method, the Phox(S) locus was cytologically estimated to be at the location 55-A on the right arm of the second chromosome and 79.6 genetically. These data show that PHOX-S is an electrophoretic variant of MOX and that PHOX-S is the first thermolabile protein found in invertebrate prophenol oxidase.