The magnetic structure of NiWO4 has been determined from neutron-diffraction measurements on single-crystal specimens. It is a collinear anti-ferromagnet in which the nickel ions have moments of 2.25 ± 0.04 μB at 19.4 ± 2.6° to the c axis in obtuse β. The form factor of the Ni++ ions follows closely the free-ion form factor. CoWO4 is shown to have an isomorphous magnetic structure.
Reactive oxygen species are the unwanted by-products
of aerobic metabolism. To protect cells against
their potentially lethal effects a series of pathways have
evolved that are collectively called the oxidative defence
system. In most eukaryotes, catalases and selenium-dependent glutathione peroxidases form the
front line of defence against hydroperoxide-mediated
damage. However, these activities are lacking in members
of the Trypanosomatidae family of protozoan
parasites. Instead these organisms contain several
enzyme-mediated pathways for removal of hydroperoxides
that are centred upon the unusual thiol trypanothione.
Here we discuss the biochemical properties of
one group of these enzymes, the non-selenium glutathione-dependent peroxidases, and outline the roles
that they play in protecting the parasite against hydroperoxides
associated with biological membranes.