Functional and phylogenetic analyses of phenoloxidases from brachyuran (Cancer magister) and branchiopod (Artemia franciscana, Triops longicaudatus) crustaceans.
Arthropod phenoloxidases catalyze the melanization and sclerotization of the new postmolt exoskeleton, and they function in the immune response. Hemocyanin, phylogenetically related to phenoloxidase, can function as a phenoloxidase under certain conditions. We investigated the relative contributions of hemocyte phenoloxidase and hemocyanin in the brachyuran crab Cancer magister, using the physiological ratio at which they occur in the hemolymph, and found that hemocyte phenoloxidase has higher activity. They both convert diphenols to o-quinones, but only the hemocyte phenoloxidase is able to catalyze the conversion of monophenols to diphenols. The quaternary structure of hemocyanin affects its reactivity as phenoloxidase. We suggest that prophenoloxidase is released from hemocytes and moves across epidermis into new exoskeleton during premolt and is activated in early postmolt. In addition to functional studies, we have determined the complete cDNA sequence of C. magister hemocyte prophenoloxidase and partial sequences from the branchiopods Artemia franciscana and Triops longicaudatus. We also sequenced C. magister cryptocyanin 2 and a hemocyanin from the amphipod Cyamus scammoni and used these and other members of the arthropod hemocyanin superfamily for phylogenetic analyses. The phylogenies presented here are consistent with the possibility that a common ancestral molecule had both phenoloxidase and reversible oxygen-binding capabilities.
Terwilliger
Nora B
NB
Oregon Institute of Marine Biology, University of Oregon, PO Box 5389, Charleston, 97420, USA. nterwill@darkwing.uoregon.edu
Ryan
Margaret C
MC
D000595:Amino Acid Sequence; D000818:Animals; D001156:Artemia / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D003386:Brachyura / Q000201:enzymology* / Q000235:genetics; D006434:Hemocytes / Q000201:enzymology; D008297:Male; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000235:genetics*; D010802:Phylogeny; D012313:RNA / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment
D012313:RNA; D014442:Monophenol Monooxygenase