Phosphorylation usually occurs on serine, threonine, tyrosine and histidine residues in eukaryotic proteins. These receptors are serine/threonine kinase receptors. They cannot synthesize isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They are protein serine/threonine kinases. It catalyzes its autophosphorylation on serine/threonine and tyrosine residues. MEK is a serine/tyrosine/threonine kinase. The oxaloacetate/aspartate family of amino acids is composed of lysine, asparagine, methionine, threonine, and isoleucine. Aspartate can be converted into lysine, asparagine, methionine and threonine. GSK-3 functions by phosphorylating a serine or threonine residue on its target substrate. The active Ras protein phosphorylates several proteins, along with the serine/threonine kinase, Raf. It lacks an intracellular serine/threonine protein kinase domain and hence is a pseudoreceptor. Aspartate kinase becomes downregulated by the presence of threonine or lysine. PBD has high affinity for proteins already phosphorylated at certain serine/threonine sites. This gene encodes a member of the RSK family of serine/threonine kinases. Isoleucine forms a negative feedback loop with threonine dehydrogenase.