Aminotransferase from a deletion mutant in the histidine operon.

The imidazolylacetolphosphate:l-glutamate aminotransferase from the deletion mutant hisHB22 has been partially characterized. Although genetic studies have not yet shown the deletion to involve the structural information for this enzyme, physical studies indicate that an abnormal enzyme is produced. Evidence is presented which, together with previous data on the characterization of the enzyme, indicates that the catalytic integrity of the enzyme is intact, and that the low specific activity seen in cell extracts is due to formation of an enzyme which has a reduced coenzyme content. It is suggested that this reduced coenzyme content is due primarily to a reduced affinity of the enzyme (nascent or apo-) for its coenzyme, and that the coenzyme must be incorporated into the enzyme at the moment of synthesis for formation of a functional protein.