Structure of the cell walls of Micrococcus lysodeikticus. 3. Isolation of a new peptide dimer, N-alpha-[L-alanyl-gamma-(alpha-D-glutamylglycine)]-L-lysyl-D-alanyl-N-alpha-[L-alanyl-gamma-(alpha-D-glutamylglycine)]-L-lysyl-D-alanine.