Since the discovery of the biological relevance of rare earth elements (REEs) for numerous different bacteria, questions concerning the advantages of REEs in the active sites of methanol dehydrogenases (MDHs) over calcium(II) and of why bacteria prefer light REEs have been a subject of debate. Here we report the cultivation and purification of the strictly REE‐dependent methanotrophic bacterium Methylacidiphilum fumariolicum SolV with europium(III), as well as structural and kinetic analyses of the first methanol dehydrogenase incorporating Eu in the active site. Crystal structure determination of the Eu‐MDH demonstrated that overall no major structural changes were induced by conversion to this REE. Circular dichroism (CD) measurements were used to determine optimal conditions for kinetic assays, whereas inductively coupled plasma mass spectrometry (ICP‐MS) showed 70 % incorporation of Eu in the enzyme. Our studies explain why bacterial growth of SolV in the presence of Eu3+ is significantly slower than in the presence of La3+/Ce3+/Pr3+: Eu‐MDH possesses a decreased catalytic efficiency. Although REEs have similar properties, the differences in ionic radii and coordination numbers across the series significantly impact MDH efficiency.

Lanthanide-dependent methanol dehydrogenases show highest activity with early lanthanides.

Lanthanide biochemistry—A surprise around every corner: lanthanides as biologically essential metals. This statement was until recently, unthinkable. This minireview presents the recent developments in the emerging field of rare‐earth element biochemistry from a coordination chemist's point of view and discusses why nature might have chosen these elements to have a catalytic role in alcohol dehydrogenase enzymes as they are found in methanotrophic and methylotrophic bacteria.

We report the preparation and new insight into photophysical properties of luminescent hydroxypyridonate complexes [MIIIL]− (M = Eu or Sm) of the versatile 3,4,3-LI(1,2-HOPO) ligand (L). We report the crystal structure of this ligand with EuIII as well as insights into the coordination behavior and geometry in solution by using magnetic circular dichroism. In addition TD-DFT calculations were used to examine the excited states of the two different chromophores present in the 3,4,3-LI(1,2-HOPO) ligand. We find that the EuIII and SmIII complexes of this ligand undergo a transformation after in situ preparation to yield complexes with higher quantum yield (QY) over time. It is proposed that the lower QY in the in situ complexes is not only due to water quenching but could also be due to a lower degree of f-orbital overlap (in a kinetic isomer) as indicated by magnetic circular dichroism measurements.