Fig. 4. Phylogenetic relationships of NO synthases from arthropods, mollusk and mammals. The deduced amino acid sequences of the oxygenase domain were analyzed using ClustalW and Treeview programs. Arthropod NOS sequences form a group divergent from molluscan and mammalian NOS sequences. Within the arthropods, the land crab NOS was diverged from insects. Within Insecta, NOS sequences grouped according to major taxonomic lineages: Lepidoptera (Manduca and Bombyx), Diptera (Drosophila and Anopheles) and Hemiptera (Rhodnius). Accession numbers were the same as those given in the legend for Fig. 2.