acid and lysine of the walls but little or no diaminopimelic acid. Hydrolysis of the extract gave glucose, identified with Glucostat reagent, and two or three other sugars, which have not yet been identified. No structure was detected after treatment of walls (5mg.) with papain (2mg. in 5ml. of 0*05M-phosphate buffer, pH7.0) or with trypsin (2mg. in 5ml. of 0-05m-phosphate buffer, pH7.0).Walls (100mg.) from the 31 hr. culture were suspended in 6M-urea (50ml.) at 200 for lhr. and then recovered by centrifuging as before. The urea extract was dialysed against distilled water and freeze-dried. Electron microscopy of the residual walls showed that some but not all of the structure had been removed. The extract contained thin layers or strings of structural material (see Plates lc and ld). Prolonged extraction (20°for 30hr.) caused complete disintegration of the walls.Walls (77mg.) were suspended in water (lOOml.) at 1000 for 25min. They were then centrifuged and freeze-dried; these 'boiled' walls (71mg.) did not show fine structure. A sample (23.7mg.) was stirred with 6M-urea solution (12ml.) at 200 for lhr. The remaining walls were centrifuged and washed with water (yield, 12mg.); areas possessing regular structure were observed on some of these walls.
The esters of z-and P-aspartyl peptides (types I1 and X ; n = 1) have been converted by alkaline hydrolysis into mixtures of acidic aspartyl peptides of types (V) and (VI). In all cases studied, the former product preponderates.The rearrangement has been shown to occur by cyclisation to the related imides (IV) followed by hydrolysis. Esters of glutamyl peptides are rearranged in a similar way, but certain differences from the asparty1 analogues have been discovered. The possible application of this rearrangement in a scheme for the specific fission of a peptide chain a t the aspartic and glutamic residues is discussed.A PEPTIDE may be degraded for structural study by partial hydrolysis with acids or enzymes, or by stepwise removal of amino-acid residues from the ends of the chain. Advances in these fields were reviewed in 1952 by Khorana (Quart. Reviews, 6, 340) and several more recent contributions have been made (e.g.,
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