Abstract
Why metalloenzymes often show dramatic changes in their catalytic activity when subjected to chemically similar but non-native metal substitutions is a long-standing puzzle. Here, we report on the catalytic roles of metal ions in a model metalloenzyme system, human carbonic anhydrase II (CA II). Through a comparative study on the intermediate states of the zinc-bound native CA II and non-native metal-substituted CA IIs, we demonstrate that the characteristic metal ion coordination geometries (tetrahedral for Zn2+, tetrahedral to octahedral conversion for Co2+, octahedral for Ni2+, and trigonal bipyramidal for Cu2+) directly modulate the catalytic efficacy. In addition, we reveal that the metal ions have a long-range (~10 Å) electrostatic effect on restructuring water network in the active site. Our study provides evidence that the metal ions in metalloenzymes have a crucial impact on the catalytic mechanism beyond their primary chemical properties.
Complexes of 1,2-bis(8-quinolylmethyleneimino)ethane with cobalt(II), nickel(II),
and copper(II) are described. The copper complexes are five-covalent and, it is
suggested, trigonal bipyramidal. Reaction of the Schiff base with iron(II),
cobalt(III), and, under certain conditions, nickel(II) leads to its partial
hydrolysis, and complexes of the tridentate 1-amino-2-(8-quinolylmethyleneimino)ethane
are obtained. The hydrolysis of the Schiff base in the presence of metal ions
is discussed in terms of steric effects within the base and of the
stereochemical demands of the metal ions.
Complexes of 1,2-bis(8-quinolylmethyleneimino)benzene
and its hydrolysis derivative 1-amino-2-(8-quinolylmethyleneimino)ethane are
also described.
Elucidating the role of metal ions in carbonic anhydrase catalysis