REMOVAL OF THE N-TERMINAL RESIDUE OF A PROTEIN AFTER TRANSAMINATION.

1. Pseudomonas cytochrome c-551 was modified by treatment at 20 degrees with glyoxylate in the presence of pyridine and cupric sulphate. The change in its chromatographic properties was consistent with conversion of its N-terminal residue into an oxo acyl residue by transamination. 2. The product underwent further modification on treatment with o-phenylenediamine or 4-methylphenylene-1,2-diamine in strong acetate buffer at 37 degrees . The final product had chromatographic properties and the N-terminal residue consistent with its differing from the native cytochrome solely in the absence of the original terminal residue. 3. The nature of analogous reactions supports these interpretations of the modifications. 4. These two treatments provide a method for specific removal of the N-terminal residue of a protein. 5. The intermediate and final products were oxidized by cytochrome oxidase at about the same rate as the original cytochrome.