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![[Figure 4]](gi5011fig4mag.jpg)
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Figure 4
The active site of human native and recombinant ALAD. Electron density contoured at 1.0 r.m.s. for the active sites of the A and B subunits of human native ALAD is shown in (a) and (b), respectively. The A subunit has an additional feature of electron density for a ligand, which we have putatively interpreted as a substrate molecule (ALA) bound by a Schiff base to Lys252. The active sites of the A and B subunits of the human recombinant enzyme are shown in (c) and (d), respectively, contoured at the same level. The recombinant enzyme has better definition of the zinc-binding cysteines in both subunits but lacks a bound substrate molecule. Note that the dative bonding to the zinc ion (grey) is only drawn in (a) since this structure possesses electron density for the full complement of tetrahedral ligands, the fourth ligand being a water molecule. |
![[Figure 4]](gi5011fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
