Prophenol oxidase A3 in Drosophila melanogaster:: Activation and the PCR-based cDNA sequence

Phenol oxidase exists in Drosophila hemolymph as a prophenol oxidase, A(1) and A(3), that is activated in vivo with a native activating system, AMM-1, by limited proteolysis with time. The polypeptide in purified prophenol oxidase A(3) has a molecular weight of approximately 77,000 Da. A PCR-based cDNA sequence coding A(3) has 2501 bp encoding an open reading frame of 682 amino acid residues. The potential copper-binding sites, from Trp-196 to Tyr-245, and from Asn-366 to Phe-421, are highly homologous to the corresponding sites in other invertebrates. The availability of prophenol oxidase cDNA should be useful in revealing the biochemical differences between A(1) and A(3) isoforms in Drosophila melanogaster that are refractory or unable to activate prophenol oxidase.