FIG. 4.

Hyg21-catalyzed phosphorylation of a diastereomeric mixture of 5‴-dihydrohygromycin A (compounds 2a and 2b). (A) HPLC chromatogram of a control reaction of dihydrohygromycin A and ATP without Hyg21. (B) HPLC chromatogram of a reaction of dihydrohygromycin A and ATP after incubation with Hyg21. Compound 2a is the naturally occurring isomer also detected in fermentation broths of the wild type and the hyg26 blocked mutant. Compound 2b is the non-natural isomer observed only in the diastereomeric mixture after chemical reduction of HA. The phosphorylated products of compounds 2a and 2b are labeled as compounds 2a-P and 2b-P, respectively.