TABLE 2.

Molecular masses and proposed structures for muropeptides present (roman numbers) and absent (arabic numbers) from the peptidoglycan of the MD003 mutant strain

Peaka	Mass (M+Na)+		Identificationc
	Observed	Calculatedb
6	NDd	990.46	Penta
10	NDd	1105.49	Penta-D
12	NDd	1104.50	Penta-N
I	1020.52	NAe	Tetra/Gly-D
II	1106.48	1106.49	Penta/d -Lac-D
III	1105.55	1105.51	Penta/d -Lac-N
25	NDd	2097.95	Penta-N-Tetra-Df
27	NDd	2096.96	Penta-N-Tetra-N
IV	2098.95	2098.95	Penta/d -Lac-N-Tetra-Df
V	2012.89	NAe	Tetra/Gly-N-Tetra-Df
VI	2011.99	NAe	Tetra/Gly-N-Tetra-N
VII	2097.86	2097.97	Penta/d -Lac-N-Tetra-N
35b	NDd	3090.42	Penta-N-Tetra-N-Tetra-Df
36	NDd	3089.44	Penta-N-Tetra-N-Tetra-N
VIII	3091.31	3091.42	Penta/d -Lac-N-Tetra-N-Tetra-Df
IX	3090.41	3090.44	Penta/d -Lac-N-Tetra-N-Tetra-N
39	NDd	4081.90	Penta-N-Tetra-N-Tetra-N-Tetra-N

^a Peak numbers refer to Fig. 4.

^b Sodiated molecular ions were the most abundant on MALDI-TOF mass spectra for all muropeptides. m/z values correspond to monoisotopic masses.

^c Penta, disaccharide pentapeptide (l-Ala-d-iGln-l-Lys-d-Ala-d-Ala; iGln is iso-glutamine); Tetra, disaccharide tetrapeptide (l-Ala-d-iGln-l-Lys-d-Ala); Tetra/Gly, disaccharide tetrapeptide (l-Ala-d-iGln-l-Lys-Gly); Penta/d-Lac, disaccharide pentadepsipeptide (l-Ala-d-iGln-l-Lys-d-Ala-d-Lac); disaccharide, GlcNAc-MurNAc; D, d-Asp; N, d-Asn; iGln, α-amidated isoGlu (or γGlu).

^d ND, not determined. MALDI-TOF masses were determined only for MD003; structures from the control peptidoglycan were assigned by comparing peaks with retention times observed for the corresponding muropeptides previously identified in the parental strain MG1363 (14).

^e NA, not applicable.

^f Positions of N and D in peptide chains of oligomeric forms are arbitrarily given.