Amino acids are designated either L or D depending on relative group arrangements around the stereogenic carbon center. L/D designations are not related to S/R absolute configurations. Only L configured amino acids are found in biological organisms. All amino acids except for L-cysteine have an S configuration and glycine is non-chiral.
In general, all L designated amino acids are enantiomers of their D counterparts except for isoleucine and threonine which contain two carbon stereocenters, making them diastereomers.