Pepsin fragmentation resolution

JT-Ray studies on the F a fragnients prepared by papain and pepsin fragmentation of human myeloma IgG immunoglobulins are being carried out by Poljak et /. The preparation of heavy-atom derivatives has involved considerable difficulties. A 6A electron-density map has been computed, which shows two clear domains (unpublished work) and is clearly of good quality. The data have been collected to 3.S A resolution, refinement of the heavy-atom positions of the derivatives has been completed, and an electron-density map computed. 

To localize the rate of deuterium buildup to specific amides, the analyte protein is fragmented into a collection of peptides using combinations of endo- and exoproteases. Due to the low pH of the quench conditions in which the protein and peptide samples are maintained after deuterium labeling, acid-reactive proteases such as pepsin must be employed. Studies with combinations of acid-reactive en-doproteinases and carboxypeptidases have been employed to achieve greater sequence coverage and higher amide resolution [42, 45]. 

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