To examine functions of two small heat shock proteins of Escherichia coli, IbpA and IbpB, we constructed His–IbpA and His–IbpB, in which a polyhistidine tag was fused to the N-terminals. Both purified His–IbpA and His–IbpB formed multimers, which have molecular masses of about – MDa and consist of about 100–150 subunits. They suppressed the inactivation of several enzymes including citrate synthase and 6-phosphogluconate dehydrogenase by heat, potassium superoxide, hydrogen peroxide and freezethawing, but not the inactivation of glyceraldehyde-3phosphate dehydrogenase by hydrogen peroxide
