Aspartokinase (or Aspartate kinase)'s an enzyme that catalyzes the phosphorylation of the amino acid aspartate. This reaction's the first step in the biosynthesis of three essential amino acids: methionine, lysine, and Threonine, known as the "aspartate family". The gene for aspartokinase's present only in microorganisms and plants; it isn't present in animals, who must obtain aspartate-family amino acids in their diet. In E. coli, aspartokinase's present as three independently regulated isozyme… (More on Aspartokinase)