A pyridoxal-phosphate protein that catalyzes the deamination of threonine to 2-ketobutyrate and ammonia. The role of this enzyme can be biosynthetic or biodegradative. In the former role it supplies 2-ketobutyrate required for isoleucine biosynthesis, while in the latter it is only involved in the breakdown of threonine to supply energy. This enzyme was formerly listed as EC 4.2.1.16.