Rare Amino Acids 4-Hydroxyproline,5-hydroxylysine found in collagen. 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. > Chapter 24 0Chapter 24 9 Rare Amino Acids • 4-Hydroxyproline, 5-hydroxylysine found in collagen. • D-Glutamic acid in cell walls of bacteria • D-Serine in earthworms • -Aminobutyric acid, a neurotransmitter • -Alanine, constituent of the vitamin pantothenic acid. =>