Superoxide dismutase in Drosophila melanogaster. Mutation site difference between two electromorphs

Two electrophoretically distinguishable variants of superoxide dismutase (SOD) are common in natural populations of Drosophila melanogaster. We have earlier comparatively characterized these two electromorphs, SODF and SODS. By peptide mapping in high-performance liquid chromatography (HPLC), we now show that the difference between the two electromorphs is due to the replacement of Asn-96 (SODF) by Lys-96 (SODS). It is far from clear how this replacement causes the biochemical differences (in thermostability, specific activity, and others) observed between these two forms of the enzyme.