Isolation of a bifunctional domain from the pentafunctional arom enzyme complex of Neurospora crassa.

Limited proteolysis of the arom enzyme complex of Neurospora crassa by trypsin or subtilisin yielded a stable fragment of Mr 68000. This fragment, which was purified by two-dimensional polyacrylamide-gel electrophoresis, was shown by activity staining to contain the shikimate dehydrogenase active site, and by substrate labelling with 3-dehydroquinate and NaB3H4 to contain the 3-dehydroquinase active site. The fragment thus constitutes a bifunctional domain containing the two enzymic activities that are known, from genetic evidence, to be located adjacently at the C-terminal end of the pentafunctional arom polypeptide.