Amino acid sequence of beta-galactosidase. VII. Isolation of the 24 cyanogen bromide peptides

All of the 24 eyanogen bromide peptides of /3-galactosidase have been isolated in pure form. Of these, 8 ranged in size from 2 to 15 residues and were purified by paper electrophoresis. The 16 large peptides, from 23 to 119 residues, were chromatographed at pH 5.0 on a carboxymethyl-cellulose column in 0.02 M ammonium acetate buffer containing 8 M urea. A number of peptides were obtained in pure form following Sephadex G-50 or G-75 gel filtration. Others were separated on sulfopropyl-Sephadex or diethyl-(2-hydroxylpropylaminoethyl)-Sephadex. Three large peptides were obtained in over 50% yield and several others were obtained in more than 25% yield. trapor 3 dialysis tubing was obtained from Spectrum Medical Industries, Inc., Los Angeles, CA 95054. Mixed bed resin AG501-X8 (D) was obtained from Bio-Rad Laboratories, Inc. All chemicals were reagent grade. Solutions of 10 M urea were deionized immediately before use on the mixed bed resin. Polyacrylamide disc gel electrophoresis at pH 8.9 in 8 M urea employed the method of Jovin et al. (5). The acrylamide concentration was 7.5% and no upper gel was used.