The brown alga Ascophyllum nodosum contains two different vanadium bromoperoxidases

Haloperoxidases have been detected in a variety of organisms, including bacteria, fungi, algae, and mammals. Mammalian haloperoxidases are known to be directly involved in the oxidative destruction of microorganisms. The algal bromoperoxidases are probably involved in the biosynthesis of bromometabolites, most of which show considerable bactericidal activity. From the brown seaweed Ascophyllum nodosum (order, Fucales) two different bromoperoxidases have been isolated, which both contain vanadium as an essential element for enzymic activity. The location of these two enzymes, determined by activity staining of cross-sections of algal parts, was different. Bromoperoxidase I (which has been described before) was located inside the thallus, particularly around the conceptacles, whereas bromoperoxidase II was present at the thallus surface of the alga. The molecular masses of these bromoperoxidases as judged from sodium dodecyl sulfate-gel electrophoresis were 97 and 106 kDa, respectively. Some of the enzymatic properties (pH optimum and Km for bromide) of the two enzymes were slightly different, whereas the amino acid compositions were more or less equal. The isoelectric point of the two proteins was the same, namely 5.0. On sodium dodecyl sulfate-polyacrylamide gels both enzymes could be stained with periodic acid Schiff's reagent, so both are glycoproteins. Since only bromoperoxidase II could be bound to a concanavalin A-Sepharose column, these enzymes contain different carbohydrates. Both enzymes display a considerable thermostability. However, the chemical stability of the two bromoperoxidases differed. Bromoperoxidase II could also be inactivated by dialysis at low pH and reactivation was only possible with the transition metal vanadium and not with other metal ions. The presence of vanadium in this enzyme could be established with atomic absorption spectrophotometry and electron paramagnetic resonance. The EPR signals of both bromoperoxidases, which were observed after reduction with sodium dithionite, were similar: only minor differences were observed in the hyperfine coupling. In immunoblotting experiments these two bromoperoxidases were found to cross-react, so they have common antigenic determinants.