ABSTRACT
The blue proteins are conspicuous because of their color and in several instances they have first been detected and isolated with the color as guidance. This is particularly true for the small blue proteins for which copper content and color are the only easily measurable properties. The higher plant blue proteins were observed in conjunction with enzyme purifications. The proteins have been isolated from nonphotosynthetic tissue and are thus not to be confused with Pc, present in the green parts of the plants. The blue proteins have in common a copper(II) site with specific and unusual properties which suggests that the copper environment is similar in all of them. Several new questions have been approached in connection with the study of the evolution of the small blue proteins. One is the comparison of whole families of sequences rather than individual sequences.
