Developmental changes in arginine: X amidinotransferase activity in streptomycin-producing strains of streptomyces

Among a number of microorganisms tested, only streptomycin- and hydroxystreptomycin-producing strains of Streptomyces contained high levels of the enzyme L-arginine: X amidinotransferase, so named because the physiological formamidine acceptor is not known. Of the several reactions common to known amidinotransferases, arginine: NH₂OH transamidination was chosen for exploratory assays because of its unique compatibility with both single- and double-displacement reaction mechanisms. In high-enzyme strains, Streptomyces griseus ATCC 12475, Streptomyces bikiniensis ATCC 11062, and Streptomyces griseocarneus ATCC 12628, amidinotransferase activity is low from 0–24 h of growth on complex media, but increase 30-fold within the next 24 h. Lysozyme extracts of the derepressed mycelia have the highest amidinotransferase activity yet observed in nature. Mycelia harvested at 24 h and shaken in 1% NaCl exhibit a similar activity increase; this phenotypic change is prevented by low levels of neomycin. Since earlier workers have shown that streptomycin formation follows a similar time-course, the evidence is strong that X is an early precursor of the streptidine moiety of streptomycin. Biosynthesis of netropsin probably does not involve a transamidination.

Arginine: X amidinotransferase activity is strongly inhibited in vitro by cystine, cystamine, formamidine disulfide, and the mixed disulfide of cysteine and thiourea, but not by oxidized glutathione. These inhibitions are reversed by 2-mercaptoethanol.