fragments were stabilised by reaction with 10 mg ml dtnb for 30 mins at room temperature followed by addition of a final concentration of 30 mm iodoacetamide for 30 mins at room temperature the fab tnb ac fragment produced was then purified on ultrogel aca 44 gel filtration chromatography the peptide corresponding to an immunodominant region of the major coat protein of fiv 680 711 gp40 sequence above was reduced with 0 5m dithiothreitol for 30 minutes at room temperature the reaction was terminated by the addition of 10 mm hcl the mixture was applied to a sep pak c18 cartridge millipore waters that was treated with 10 mls of a 40 60 acetonitrile hcl solution the reduced peptide was cycled three times through the sep pak washed with 20 mls of 10 mm hcl before elution with 5 mls of 40 60 acetonitrile hcl the reduced peptide was then freeze dried overnight the peptide in 34 b 34 above was dissolved in 6m guanidine hcl and mixed with the 4c1 180 fab tnb ac mixture from a above in a 0 5 1 0 1 0 peptide antibody molar ratio for 1 min at room temperature the reaction was terminated by the addition of a final concentration of 30 mm iodoacetamide for 30 mins at room temperature initial purification.