Chemistry Reference
In-Depth Information
SDR
FIGURE 12.9
Reactions catalysed by SDR enzymes.
description as a DNA repair protein). Other examples which involve reactivity of zinc cysteine thiolate linkages
include methionine synthase, and the farnesyl- and geranylgeranyl-transferases, which participate, respectively,
in the transfer of farnesyl and geranylgeranyl groups to target proteins.
MULTINUCLEAR AND COCATALYTIC ZINC ENZYMES
A number of zinc enzymes require two or more metal ions for full activity, but in the absence of X-ray structural
data the location of these metal centres with regard to one another was often uncertain. When the first three-
dimensional structures began to appear, it became clear that the metals were in close proximity. A particular
feature of many of these enzymes was the presence of a bridging ligand between two of the metal sites, usually an
Asp residue of the protein, which is occasionally replaced by a water molecule. Whereas some of the sites contain
only Zn ions, several contain Zn together with Cu (in cytosolic superoxide dismutases), Fe (in purple acid
phosphatases), or Mg (in alkaline phosphatase).
