NON-PROTEIN AMINO ACIDS
Non-protein amino acids are the ones which are not incorporated in proteins but occur freely or in combined state in non-protein substances.
Their number is more than 180.
(i) Ornithine and Citrulline threonine.
(ii) Homoserine is intermediate in synthesis of cysteine, methionine and threonine.
(iii) Diaminopimelic acid is intermediate in synthesis of lysines.
(iv) D-Alanine and D-Glutamic acid are component of peptidolycan of bacterial wall.
(v) Gamma Aminobutyric acid or GABA is a synaptic neurotransmitter that causes inhibition by opening chloride channels.
(vi) A number of antibiotics contain amino acid analogues that prevent protein synthesis, e.g., D-Phenylalanine in Gramicidin - S
(vii) Actinomycin - D, an inhibitor of RNA synthesis, contains D-Valine.