Glucose-fructose oxidoreductase, a periplasmic enzyme of Zymomonas mobilis, is active in its precursor form

Glucose-fructose oxidoreductase (GFOR) is a periplasmic enzyme of the ethanologenic, Gram-negative bacterium Zymomonas mobilis. It contains tightly bound NADP+ as cofactor. In Z. mobilis GFOR-recombinant strains, a precursor form of GFOR was accumulated. To assay the preGFOR for its NADP(H) content and enzymatic activity, it was purified from an overproducing strain. Using SDS-PAGE, the precursor subunit size was determined to approximately 45 kDa (compared with a 40 kDa subunit size for the mature GFOR subunit). The N-terminal amino acid sequence of the precursor was determined. The N-terminal residues of the GFOR matched with the signal sequence from the DNA sequence of the gene gfo. The precursor form of GFOR was enzymatically active and contained the cofactor NADP(H).