title: Role of hemoglobin from blood clam Scapharca kagoshimensis beyond oxygen transport.
abstract: The evolutionary race between hosts and pathogens has led to a variety of adaptations. Little is known about the immunological role of hemoglobin (Hb) in antimicrobial immune responses. Results showed that a 31.2 kDa monodimer Hb (skHbI) and a 57.8 kDa heterotetramer Hb (skHbII) from the blood clam, Scapharca kagoshimensis, had phenoloxidase (PO)-like activities and antimicrobial activities. Both were found capable of oxidizing l-DOPA, catechol and hydroquinone. Their PO-like activities were visibly greatly inhibited by oxidase inhibitors, EDTA, and divalent metal ions, and greatly enhanced by isopropanol and Fe(2+), indicating that they have the properties of a metalloenzyme and a catecholase-type PO as well. They also showed obvious anti-bacterial activities against gram-positive bacteria but not against either gram-negative bacteria nor fungi. The anti-bacterial activities levels were a result of the generation of reactive oxygen species (ROS) of superoxide anions. These results indicate that skHbI and skHbII, not only function as iron-containing oxygen carriers, but also exert anti-bacterial activities and catecholase-type oxidizing activities. The fact that skHbII exerts high level of PO-like activity indicates different roles in the innate immunodefense system. These results may improve understanding of the multiple functions of invertebrate Hbs beyond serving as oxygen carriers and may provide insight into how the fundamental and universal mode of the innate immune system has persisted in respiratory proteins throughout the course of evolution.
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Xu
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China; Department of Histology and Embryology, Medical College, Qingdao University, Qingdao 266021, China.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Jing
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China; Department of Biology, Medical College, Qingdao University, Qingdao 266021, China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China. Electronic address: tjfan@ouc.edu.cn.
authors.forename: Tingjun
authors.initials: T
authors.lastname: Fan
mesh_terms: D000818:Animals; D001419:Bacteria / Q000254:growth & development; D002614:Chelating Agents / Q000494:pharmacology; D005658:Fungi / Q000254:growth & development; D006454:Hemoglobins / Q000737:chemistry / Q000276:immunology* / Q000302:isolation & purification / Q000378:metabolism; D019216:Metals, Heavy / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors / Q000276:immunology* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D049894:Scapharca / Q000276:immunology* / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
chemical_list: D002614:Chelating Agents; D006454:Hemoglobins; D019216:Metals, Heavy; D013481:Superoxides; D014442:Monophenol Monooxygenase; D010100:Oxygen
keywords: Anti-bacterial activity; Hemoglobin; Phenoloxidase; Reactive oxygen species; Scapharca kagoshimensis