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

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Abstract
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 enzymes 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.