Active-site-specific zinc-depleted and reconstituted cobalt(II) human-liver alcohol dehydrogenase. Preparation, characterization and complexation with NADH and trans-4-(N,N-dimethylamino)-cinnamaldehyde.

The active-site zinc atom of the beta 1 beta 1 isozyme of class I alcohol dehydrogenase (EC 1.1.1.1) from human liver was specifically removed by the chelating agent dipicolinic acid. From beta 1 gamma 1 and gamma 1 gamma 1 isozyme the active-site zinc is extracted much more slowly than from beta 1 beta 1 isozyme. Only partially active-site metal-depleted enzyme species were obtained from these isozymes. The active-site-specific reconstituted cobalt(II) derivative of the beta 1 beta 1 isozyme shows spectroscopic properties comparable to those of the active-site-specific reconstituted cobalt(II) horse liver alcohol dehydrogenase. The coenzyme-induced conformational change of the protein leads to a red shift of the d-d band from 648 nm to 673 nm. The chromophoric substrate trans-4-(N,N-dimethylamino)-cinnamaldehyde forms ternary complexes with NADH and the different isozymes, in close analogy to horse liver alcohol dehydrogenase. The differences in the active sites between beta 1 and gamma 1 subunits (threonine-48 instead of serine-48) or between zinc and cobalt(II) are reflected in the visible absorption spectra of the metal-bound chromophoric substrate.

H8Zn(c)2 and Zn(c)2Co(n)2 human liver alcohol dehydrogenase.

The zinc ion in the noncatalytic site of human beta 1 beta 1 and beta 1 gamma 1 isozymes of class I alcohol dehydrogenases (EC 1.1.1.1) was specifically replaced by Co(II) ion. The absorption and CD spectra prove that these derivatives contain cobalt bound at the noncatalytic site to the same ligands and in the same coordination geometry as in the corresponding species obtained from the horse liver EE isozyme. These Zn(c)2Co(n)2 human liver alcohol dehydrogenases could be obtained in two ways: (a) by exchange dialysis, (b) by removal of the noncatalytic zinc and subsequent insertion of cobalt(II) ion into the empty site. The human isozymes differ from the horse liver EE enzyme in the possibility of forming stable species lacking the noncatalytic zinc ion. This difference in chemical reactivity of the noncatalytic zinc atom may be related to amino acid changes in the human isozymes, compared to horse liver alcohol dehydrogenase.

A potentiometric and spectroscopic study of the proton and copper(II) complexes of methionine enkephalin and some related ligands.

The results are reported of a potentiometric and spectrophotometric study of the proton and copper(II) complexes of methionine enkephalin and four related pentapeptides which all show greater biological activity than their parent enkephalin. Measurements were carried out at 25 degrees C and I = 0.10 mol dm-3 (KNO3). All the ligands studied form stable copper(II) complexes comparable to those formed by pentaglycine, with the peptide chain locked in a folded conformation by NNN or NNNN coordination to the metal ion. There is no indication of bonding through the tyrosine-phenolate oxygen atoms or the methionine sulfurs.

A suggested role for copper in the biological activity of neuropeptides.

We have shown that a proline residue in the second or third position of a tetrapeptide chain acts as a 'break-point' to Cu(II) coordination dividing the peptide chain into two parts which coordinate independently. Proline also encourages a beta-conformation for the peptide chain presenting the terminal residues in a suitable conformation to form an abnormally large chelate ring. Many neuropeptides contain proline residues and it is likely that Cu(II) ions assist in holding these peptide molecules in the biologically favourable beta-conformation by bridging across the ends of the chain.

Metal--glutathione interaction in aqueous solution. Nickel(II), cobalt(II) and copper(II) complexes with oxidized glutathione.

The interaction of copper(II), nickel(II) and cobalt(II) ions with oxidized glutathione in aqueous solutions have been examined by spectroscopic methods. Cu(II) is the only ion which interacts with disulphide bridge and forms dimeric species containing the Cu(II)-S-S-Cu(II) unit. Ni(II) and Co(II) bind mainly with the terminal NH2 and COO- groups of glutamic acid, and the complexes formed are of nearly octahedral symmetry. At high pH, in the Co(II)-GSSG solution Co(II) is oxidized to Co(III) with the concomitant reduction of GSSG to GSH. Considerable differences were observed between the oxidized and reduced form of glutathione in the coordination ability towards metal ions.