Die aminosäuresequenz des mureins von Microbacterium lacticum

Abstract

Cell walls of Microbacterium lacticum were purified by digestion with trypsin and extraction with trichloroacetic acid. The amino acid analysis showed that in addition to the usual amino sugars the murein (peptidoglycan) contained glutamic acid, lysine, glycine and d-alanine in the molar ratio of about 1:2:2:1, but no ammonia. The dinitrophenylation of the cell wall yielded ε-DNP-lysine (66% of the total amount of lysine). The hydrazinolysis showed that at least 40% of the lysine, 6% of d-alanine and 2.6% of glycine are C-terminal. From partial acid hydrolysate oligopeptides were isolated by paper chromatography and identified. From these data and those mentioned above, the following scheme of the amino acid sequence and mode of crosslinking of the main part of the murein could be proposed. The tetrapeptide bound to muramic acid showed the sequence Gly-Glu-Lys- d-Ala. The second mole of glycine and of lysine, respectively, is involved in the crosslinking. They form the peptide N 2-glycyllysine which is bound by its glycine end to glutamic acid and by the ε-amino group of lysine to d-alanine of an adjacent tetrapeptide. In contrast to other mureins the ε-amino group of the lysine within the tetrapeptide is free. Only about 60% of the tetrapeptides are actually crosslinked. In the other cases, the ε-amino group of the lysine is free or the crosslinking peptide is incomplete. Various data indicate that some tetrapeptides are also incomplete. In this case the C-terminal d-alanine, and sometimes also the lysine, are missing. The murein of M. lacticum resembles the unusual mureins of Butyribac- terium rettgeri and Corynebacterium poinsettiae.