Polarized light micrograph of alanine crystals, a non-essential amino acid in humans, used in the biosynthesis of proteins and involved in the metabolism of tryptophan and vitamin pyridoxine. As an amino acid, it is only second to leucine in rate of occurrence. It is present in bacterial cell walls and in some peptide antibiotics. We can find it in a wide variety of foods, and particularly concentrated in meats. Alanine plays a key role in the glucose?lanine cycle between tissues and liver. Linked to diabetes and hypertension, it is an important source of energy for muscles and the central nervous system, strengthens the immune system, and promotes lymphocyte production. It constitutes a substrate for hepatic gluconeogenesis and ureagenesis, and is also known to cause cytotoxic oxidative stress in brain tumour cells. Field of view size: 2.97 x 4.45 mm (0.117 x 0.175 in)