Structural identity between the iron- and manganese-containing superoxide dis- mutases. Protein Engn

+To whom correspondence should be addressed We have recently reported the first complete amino add se-quence of an iron-containing superoxide dismutase. Hie iron enzyme is thought to be closely homologous to the man-ganese-containing superoxide dismutases. The availability of complete amino add sequence information for four mangan-ese superoxide dismutases and the crystal structures for two iron and two manganese superoxide dismutases prompted us to investigate the degree of homology between the two pro-teins at various levels. We report that it is not possible to clear-ly distinguish the two proteins on the basis of their secondary or tertiary structures. It would appear that a small number of single site substitutions are responsible for conferring distinguishing properties between the two proteins. Substitu-tion of glyclne 77 and ghitamine 154 by a ghitamine and an alanine respectively in Photobacterium leiognathi iron superox-ide dismutase may distinguish the kinetic and other particular properties of this protein from the manganese protein (and other iron superoxide dismutases). Furthermore the primary structure of both the iron and manganese proteins does not appear to have any homology with any other known amino add sequence. Key words: iron/manganese/superoxide dismutase/amino acid se-quence/secondary structure/crystal structur