(A) Elution profile of standard proteins and AR-B peptide from Superdex 75. Purified AR-B was chromatographed on Superdex 75 (1.6 by 40 cm) as described in Materials and Methods and compared to the elution of the standard proteins bovine serum albumin (66 kDa), carbonic anhydrase (29 kDa), cytochrome c (12.4 kDa), and aprotinin (6.4 kDa). (B) Native gel electrophoresis of S. gordonii SspB protein. Purified SspB protein (15 μg) was electrophoresed in a 4 to 15% gradient PhastGel with native gel buffer strips. Native size standards were thyroglobulin (660 kDa), ferritin (440 kDa), catalase (232 kDa), lactate dehydrogenase (140 kDa), and bovine serum albumin (66 kDa).