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Vanadium haloperoxidases contain the bare metal oxide vanadate as a prosthetic group and differ strongly from the heme peroxidases in substrate specificity and molecular properties. The substrates of these enzymes are limited to halides and sulfides, which in the presence of hydrogen peroxide are converted into hypohalous acids or sulfoxides, respectively. Several seaweeds contain iodo- and bromoperoxidases and their direct or indirect involvement in the production of the huge amounts of brominated, iodinated compounds and the formation of I2 in the marine environment will be reviewed. Vanadium chloroperoxidases occur in a group of common terrestrial fungi and are probably involved in the degradation of plant cell walls and breakdown of the leaf cuticle. The natural presence of high-molecular-weight chloro-aromatics in the environment is probably be due to the activity of these enzymes. Based upon several X-ray structures of the enzymes and detailed kinetics a molecular mechanism is proposed and discussed in detail. As will be shown the metal oxide in the active site binds hydrogen peroxide in a side-on fashion and acts as a Lewis acid allowing nucleophilic attack of an incoming halide and formation of HOX. The surprising evolutionary relationship between the bacterial and mammalian acid phosphatases that hydrolyze phosphate monoesters and the vanadium haloperoxidases will be shown.

The labeling of fish with radioisotopes is a useful technique for analyzing specific features of development, although contamination by the radioisotope may cause some problems. In the present experiments, an activable element stable samarium was administered to fish by injection or by feeding. The element may then be accumulated in certain tissues. Only when the sample containing stable samarium is bombarded with thermal neutrons, the radioisotope, ^Sm, is produced and can be detected. The purpose of the present experiments was to confirm the possibility of labeling fish with samarium and to determine in which tissues the element is specifically accumulated.