<P> Biosynthetic pathways are often highly regulated such that building - blocks are synthesized only when supplies are low . Very often, a high concentration of the final product of a pathway inhibits the activity of enzymes that function early in the pathway . Often present are allosteric enzymes capable of sensing and responding to concentrations of regulatory species . These enzymes are similar in functional properties to aspartate transcarbamoylase and its regulators . Feedback and allosteric mechanisms ensure that all twenty amino acids are maintained in sufficient amounts for protein synthesis and other processes . </P> <P> Microorganisms use ATP and reduced ferredoxin, a powerful reductant, to reduce atmospheric nitrogen (N) to ammonia (NH). An iron - molybdenum cluster in nitrogenase deftly catalyzes the fixation of N, a very inert molecule . Higher organisms consume the fixed nitrogen to synthesize amino acids, nucleotides, and other nitrogen - containing biomolecules . The major points of entry of ammonia into metabolism are glutamine or glutamate . </P> <P> Most amino acids are synthesized from α - ketoacids, and later transaminated from another amino acid, usually glutamate . The enzyme involved in this reaction is an aminotransferase . </P> <Dl> <Dd> α - ketoacid + glutamate ⇄ amino acid + α - ketoglutarate </Dd> </Dl>

Where are non essential amino acids made in the body