You discover that you suffer from a deficiency in the amino acid tryptophan.At the pharmacy,you find both d-tryptophan and l-tryptophan supplements.Which do you purchase? Why?

You should choose l-tryptophan.All amino acids can exist as one of two stereoisomers (d or l)because of asymmetry around the α carbon.Proteins consist of the l form of amino acids,and as these stereoisomers possess distinct biological properties and are not readily interconverted,you should choose the form that is normally utilized by cells.