Catalyzes two non-consecutive transamidination reactions. It converts scyllo-inosamine 4-phosphate into N-amidino-scyllo-inosamine 4-phosphate and N1-amidinostreptamine 6-phosphate into streptidine 6-phosphate (By similarity). 1-amino-1-deoxy-scyllo-inositol 4-phosphate + L-arginine = 1-guanidino-1-deoxy-scyllo-inositol 4-phosphate + L-ornithine Antibiotic biosynthesis; streptomycin biosynthesis. Homodimer. Belongs to the amidinotransferase family.