I wish to report the demonstration in a cell-free extract from Escherichia coli of an enzyme capable of transposing groups on both asymmetric carbon atoms of threonine to convert D- threonine to L-threonine, for which ATP or yeast or muscle adenylic acid serves as a cofactor. In rather limited attempts it has not been possible to demonstrate a vitamin B6 requirement. Cells of Escherichia coli, strain K-12, grown on the medium of Davis and ...
