Abstract
1. The intermediary product between homoserine and threonine, synthesized enzymatically from homoserine and ATP in the presence of Mg_??_, was isolated as barium salt and identified as O-phosphohomo-serine.
2. The over-all reaction leading to the synthesis of threonine has been formulated as homoserine→O-phosphohomoserine→threonine. The postulated pathway was also supported by the studies on phosphate transfer.
