Construction and characterization of a recombinant tripartite enzyme, galactose dehydrogenase/beta-galactosidase/galactokinase.

The in-frame gene fusion between 3 enzymes, galactose dehydrogenase, beta-galactosidase and galactokinase, is described. The purified artificial tripartite enzyme displayed all three enzymic activities. Two major forms of the hybrid protein were found, consisting of 4 and 8 subunits respectively, but other forms could also be identified. Each subunit was made up of one monomer each of galactose dehydrogenase, beta-galactosidase and galactokinase. Proximity effects exhibited by the hybrid enzyme could be demonstrated using [14C]galactose as a reporter molecule.