ATP:inosamine phosphotransferase(s)

Presence of strA-strB gene within a streptomycin-resistance operon in a clinical isolate of Shigella flexneri

Three aminoglycoside-modifying enzymes (AMEs) were produced by a clinical isolate of Shigella flexneri which was resistant to gentamicin, tobramycin, netilmicin, kanamycin, sisomicin and streptomycin: acetyltransferase (AAC) (3)-II-type, and phosphotransferase (APH) (3")- and (6)-type enzymes. The aminoglycoside-resistance genes were located on a 75-Kb plasmid. Two genes, strA-HK and strB-HK, in a transcriptional unit were found to code for streptomycin-resistance. The genetic organization and sequence of this transcriptional unit were identical to those of strA and strB in plasmid RSF1010. strA-HK and strB-HK when expressed separately produced functional enzymes. Our substrate profile study on the crude extracts of StrA-HK and StrB-HK proteins confirmed that StrA-HK was an APH(3")-type and showed that StrB-HK was a member of the APH(6) family.

Biosynthesis of streptomycin. Purification and properties of a dTDP-L-dihydrostreptose: streptidine-6-phosphate dihydrostreptosyltransferase from Streptomyces griseus

dTDP-L-dihydrostreptose: streptidine-6-phosphate dihydrostreptosyltransferase, an enzyme involved in the biosynthesis of streptomycin, has been purified from Streptomyces griseus to near homogeneity by a six-step procedure involving chromatography on streptidine-6-phosphate-Sepharose. By gel filtration the apparent Mr of the enzyme was found to be about 63 000. The subunit Mr found on sodium dodecylsulfate gels is about 35 000. The transferase is dependent on Mn2+ or Mg2+ ions. Co2+ is as effective as Mg2+. From the substrates tested only streptidine 6-phosphate was an acceptor for dihydrostreptose in the synthesis of O-alpha-L-dihydrostreptose(1 leads to 4)-streptidine 6-phosphate. No activity was found with streptidine, 2-deoxystreptamine and 4-deoxy-streptamine. The activity of the transferase in the course of fermentation runs parallel to the activity of dTDP-dihydrostreptose synthase and reaches a maximum after around 50 h of fermentation, just before appearance of streptomycin in the medium.