Superoxide dismutase from Bacillus stearothermophilus: reversible removal of manganese and its replacement by other metals [proceedings].

reacted with other reactive groups in the protein. However, it would appear that, whatever other reactions may have occurred, the increase in specifically monitors the extent of modification of histidine residues only. Thus diethyl pyrocarbonate appears to have reacted with pig pepsinogen to modify, at least, all three histidine residues in the protein. Once again, therefore, the potential activity observed of 30% must be inherent in the completely modified protein and cannot be derived from molecules which have undergone only fractional modification. Since both of these types of reaction produce derivatives which are virtually completely modified but which possess only a fraction of the potential activity of native pepsinogen, derivatives could be used to study further the activation process. They may activate themselves more slowly than unmodified pepsinogen, and this would facilitate following the course of activation.