The invention provides a novel method of analysing the proteome of a cell. The method allows the correlation of expression of proteins with the activity of compartments in the cell and the association of thus far unidentified proteins with(in) such compartments. This gives the artisan a powerful tool in the elucidation of the function of proteins thus identified. According to this method a new family of proteins was identified and the function thereof determined and confirmed by experiments. The family termed smERp belongs to the oxidoreductase proteins, but is distinct therefrom in their activity and internal structure. The invention further identifies several other proteins and their function, together with methods wherein the identified proteins can be manipulated to obtain, or gain further functionality. The invention also provides methods wherein proteins identified in the present invention are used for the production of proteins of interest.