Reactive Amino Groups in Baker's Yeast Cytochrome c

Abstract

The cysteine residue in baker's yeast cyto-chrome c consisting of 108 amino acid residues was quantitatively substituted with N-ethyl-maleimide without an appreciable decrease of the activity. On incubation of the modified cytochrome with trinitrobenzene sulfonate at 0°C, the N-terminal a-amino group (the -5th position) reacted first and then four lysine residues at the 4th, 89th, 100th and an unknown positions with almost the same reactivities. The activity of the modified cytochrome decreased with the increase of the number of the introduced trinitrophenyl group. Although the participation of the three lysine residues in the activity could not clearly be demonstrated, the sulfhydryl and the α- and s-amino groups of the N-terminal and the above four lysine residues were concluded to be exposed on the surface of the cytochrome molecule.
The authors express their sincere thanks to Sankyo Co. Ltd., for providing us of baker's yeast cytochrome c and to Dr. K. Wada for the assay of cytochrome oxidase activity of the modified derivatives of the cytochrome c.