Biosynthesis of 2-deoxystreptamine

Extracts of Streptomyces fradiae 75-078, a producer of an antibiotic neomycin, were found to catalyze three reactions which are included in the proposed biosynthetic pathway to 2-deoxystreptamine; amination of deoxyinosose yielding deoxyinosamine, conversion of deoxyinosamine to 2-deoxystreptamine and deamination of 2-deoxystreptamine. Glutamine was effective as an amino-donor for both transamination reactions; conversions of deoxyinosose to deoxyinosamine and of aminodeoxyinosose to 2-deoxystreptamine. Conversion of deoxyinosamine to 2-deoxystreptamine, presumably including successive dehydrogenation and transamination at position 1, was stimulated by NAD+. On DEAE-Sepharose CL-6B ion-exchange chromatography, the enzyme activity catalyzing amination of deoxyinosose and deamination of 2-deoxystreptamine was eluted as an entity (aminotransferase), while the one converting deoxyinosamine to 2-deoxystreptamine, only if the aminotransferase is supplemented, can be eluted as a separate peak (deoxyinosamine dehydrogenase). The molecular weight of the aminotransferase was estimated to be 130,000 daltons by chromatography on Sepharose CL-6B. Enzymatic synthesis of 2-deoxystreptamine from deoxyinosose was demonstrated by the cell free extracts.