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Mg-chelatase catalyzes the insertion of Mg 2þ into protoporphyrin IX at the first committed step of the chlorophyll biosynthetic pathway. It consists of three subunits: I, D, and H. The I subunit belongs to the AAA protein superfamily (ATPases associated with various cellular activities) that is known to form hexameric ring structures in an ATP-dependant fashion. Dominant mutations in the I subunit revealed that it functions in a cooperative manner. We demonstrated that the D subunit forms ATP-independent oligomeric structures and should also be classified as an AAA protein. Furthermore, we addressed the question of cooperativity of the D subunit with barley (Hordeum vulgare) mutant analyses. The recessive behavior in vivo was explained by the absence of mutant proteins in the barley cell. Analogous mutations in Rhodobacter capsulatus and the resulting D proteins were studied in vitro. Mixtures of wild-type and mutant R. capsulatus D subunits showed a lower activity compared with wild-type subunits alone. Thus, the mutant D subunits displayed dominant behavior in vitro, revealing cooperativity between the D subunits in the oligomeric state. We propose a model where the D oligomer forms a platform for the stepwise assembly of the I subunits. The cooperative behavior suggests that the D oligomer takes an active part in the conformational dynamics between the subunits of the enzyme.

We experimentally evaluated the impact of the introduced signal crayfish (Pacifastacus leniusculus) and the native noble crayfish (Astacus astacus) on eggs and larvae of seven species of amphibians, likely to co-occur with crayfish in southern Sweden. In aquarium experiments eggs and tadpoles of all amphibian species were consumed by both crayfish species. The consumption of amphibian eggs by signal crayfish increased with temperature. The noble crayfish consumed more tadpoles than the signal crayfish, but the latter caused more sub-lethal damage to tadpoles. Tadpoles of the common toad (Bufo bufo) were sometimes killed but left uneaten by both crayfish species. In pool experiments, signal crayfish consumed more tadpoles of Hyla arborea in a less complex habitat and significantly reduced survival of Hyla tadpoles and the biomass of aquatic macrophytes.

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