Rare Amino Acids 4-Hydroxyproline,5-hydroxylysine found in collagen胶原， D-Glutamic acid in cell walls of bacteria. D-Serine in earthworms. y-Aminobutyric acid,a neurotransmitter. B-Alanine,constituent of the vitamin pantothenic acid泛酸.Rare Amino Acids ◼4-Hydroxyproline, 5-hydroxylysine found in collagen胶原 . ◼D-Glutamic acid in cell walls of bacteria. ◼D-Serine in earthworms. ◼-Aminobutyric acid, a neurotransmitter. ◼-Alanine, constituent of the vitamin pantothenic acid泛酸