Premium
Models for Active Sites of Metalloenzymes: Comparison of Zinc and Beryllium Containing Complexes
Author(s) -
Osman Roman,
Weinstein Harel
Publication year - 1980
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198000015
Subject(s) - chemistry , active site , carboxypeptidase a , metal , ligand (biochemistry) , zinc , crystallography , transition metal , computational chemistry , stereochemistry , carboxypeptidase , catalysis , organic chemistry , enzyme , biochemistry , receptor
Metal containing models of the active site of the metalloenzyme carboxypeptidase were studied by quantum chemical ab initio calculations. The comparative properties of [Zn(OH)(NH 3 ) 2 ] + and [Be(OH)(NH 3 ) 2 ] + indicate some of the characteristics of the role of transition metals in biological systems: the Zn complex, but not the Be complex, generates directionality constraints for an incoming ligand that are compatible with the geometrical features identified in the crystal structure of the active site — substrate complex. Moreover, an incoming ligand (H 2 O) is perturbed more strongly by the Zn complex than by the Be complex. This perturbation (a charge transfer and a characteristic polarization of the electronic density along the metal–ligand axis) is in good agreement with the proposed effect of the metal in the active site on the reactivity of a carbonyl carbon in a peptide bond. The perturbation caused by the incoming ligand in the electronic structure of the metal containing complex is also larger for the Zn complex than for the Be complex. These findings indicate that while the Be complex may simulate some of the purely electrostatic effects of the Zn containing model of the active site, it does not represent as well as the Zn complex some of the reactivity elements that have been implicated in the role of the metal in the catalytic mechanism of carboxypeptidase.