Purification and cloning of the salivary peroxidase/catechol oxidase of the mosquito Anopheles albimanus.

Salivary homogenates of the adult female mosquito Anopheles albimanus have been shown previously to contain a vasodilatory activity associated with a catechol oxidase/peroxidase activity. We have now purified the salivary peroxidase using high-performance liquid chromatography. The pure enzyme is able to relax rabbit aortic rings pre-constricted with norepinephrine. The peroxidase has a relative molecular mass of 66 907 as estimated by mass spectrometry. Amino-terminal sequencing allowed us to design oligonucleotide probes for isolation of cDNA clones derived from the salivary gland mRNA from female mosquitoes. The full sequence of the cDNA demonstrated homology between A. albimanus salivary peroxidase and several members of the myeloperoxidase gene family. A close comparison of A. albimanus salivary peroxidase with canine myeloperoxidase, for which the crystal structure is known, showed that all six disulfide bridges were conserved and demonstrated identity for all five residues associated with a Ca2+-binding site. In addition, 16 of 26 residues shown to be in close proximity to the heme moiety in the canine myeloperoxidase were identical. We conclude that the salivary peroxidase of A. albimanus belongs to the myeloperoxidase gene family. Other possible functions for this molecule in blood feeding are discussed.