L-threonine + L-serine => L-seryl-L-threonine + H2O
l-threonine + l-serine => l-seryl-l-threonine + h2o
L-threonine + L-serine => L-seryl-L-threonine + H2O
l-threonine + l-serine => l-seryl-l-threonine + h2o