Transaminase Activity in Neurospora crassa

It is now believed that the amino groups of isoleucine and valine are accepted by their respective carbon chains during biosynthesis via a transamination. Most of the evidence for this hypothesis has been derived from experiments on isoleucineless and valineless mutants of Escherichia coli and Neurospora crassu (l-4). It is not positively established whether this transamination step can be mediated for both amino acids by a single enzyme or, contrarily, whether each of the keto acid precursors reacts with a separate specific transaminase. Wagner and Ifland (5), on the basis of results derived from crude preparations, proposed that the anomalous behavior of the mutant, T-77 of Neurospora, might be due to a qualitative change in isoleucine-valine transaminase. The experiments reported here were designed to investigate the behavior of a purified transaminase preparation with respect to valine, isoleucine, and their respective Lu-keto acids. Mutant T-77 and wild type Neurospora were re-examined.