Structure of 6-phosphogluconate dehydrogenase from sheep liver at 6 Å resolution

Abstract

A 6 A resolution electron density map has been calculated for 6-phosphogluconate dehydrogenase from sheep liver. The dimeric enzyme crystallizes with a single subunit in the asymmetric unit. The structure was determined by the method of isomorphous replacement. The two heavy-atom derivatives used were obtained by soaking crystals in potassium dicyanoaurate, which bound at two sites, and potassium tetracyanoplatinate, which bound at three different sites in the monomer. The resulting electron density map shows the molecular boundary and indicates which of the crystallographic 2-fold axes is the molecular 2-fold. The subunit is ellipsoidal with a large indentation distant from the subunit boundary. Several columns of density of the correct dimensions for α-helices can be seen. Some of these are a part of the subunit contact area and two are more than 40 A units long.