Purification and properties of the aromatic (arom) synthetic enzyme aggregate of Neurospora crassa

1. Procedures are described for the purification of the wild type arom multienzyme complex encoded in the arom gene cluster of Neurospora crassa.

2. The purified aggregate has all five activities present at high levels and there has been no indication that the five activites are separable during purification.

3. The enzyme is readily inactivated by O2 even in the presence of thiols.

4. The molecular weight of the purified aggregate is estimated to be approx. 231 000 on the basis of data from equilibrium sedimentation and amino acid analysis.

5. Experiments on disruption of the purified aggregate (which leads to loss of enzymic activities) and on renaturation (which restores three of the five activities), together with independent studies of allelic complementation, suggest that the complex consists of two identical halves bound together by relatively weak non-peptide bonds.

6. Preliminary evidence has also been obtained for the presence of still smaller components, possibly representing the five different polypeptide chains which are thought to be the basis of subunits of which the aggregate is composed.