Aspartokinase (or Aspartate kinase) is an enzyme that catalyzes the phosphorylation of the amino acid aspartate. This reaction is the first step in the biosynthesis of three essential amino acids: methionine, lysine, and Threonine, known as the "aspartate family". The gene for aspartkinase is 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 is present as three independently regulated isoz… (More on Aspartokinase)